US20110043080A1 - Complex resonance circuit and oscillation circuit using the same - Google Patents
Complex resonance circuit and oscillation circuit using the same Download PDFInfo
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- US20110043080A1 US20110043080A1 US12/926,224 US92622410A US2011043080A1 US 20110043080 A1 US20110043080 A1 US 20110043080A1 US 92622410 A US92622410 A US 92622410A US 2011043080 A1 US2011043080 A1 US 2011043080A1
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/54—Filters comprising resonators of piezo-electric or electrostrictive material
- H03H9/545—Filters comprising resonators of piezo-electric or electrostrictive material including active elements
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
- H03B28/00—Generation of oscillations by methods not covered by groups H03B5/00 - H03B27/00, including modification of the waveform to produce sinusoidal oscillations
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
- H03B5/00—Generation of oscillations using amplifier with regenerative feedback from output to input
- H03B5/30—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element being electromechanical resonator
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
- H03B5/00—Generation of oscillations using amplifier with regenerative feedback from output to input
- H03B5/30—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element being electromechanical resonator
- H03B5/32—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element being electromechanical resonator being a piezoelectric resonator
- H03B5/36—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element being electromechanical resonator being a piezoelectric resonator active element in amplifier being semiconductor device
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/25—Constructional features of resonators using surface acoustic waves
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/54—Filters comprising resonators of piezo-electric or electrostrictive material
- H03H9/56—Monolithic crystal filters
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/54—Filters comprising resonators of piezo-electric or electrostrictive material
- H03H9/56—Monolithic crystal filters
- H03H9/566—Electric coupling means therefor
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/64—Filters using surface acoustic waves
- H03H9/6423—Means for obtaining a particular transfer characteristic
- H03H9/6433—Coupled resonator filters
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
- H03J3/00—Continuous tuning
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
- H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
- H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
- H03H3/04—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks for obtaining desired frequency or temperature coefficient
- H03H2003/0414—Resonance frequency
- H03H2003/0464—Resonance frequency operating on an additional circuit element, e.g. a passive circuit element connected to the resonator
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- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Chemical & Material Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Theoretical Computer Science (AREA)
- Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
- Oscillators With Electromechanical Resonators (AREA)
- Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
Abstract
A piezoelectric vibration device includes a single piezoelectric substrate, at least three electrode pairs formed on the single piezoelectric substrate, and two external connection terminal pairs, wherein the three electrode pairs are connected to the two external connection terminal pairs so that two different vibration modes individually appear at the two external connection terminal pairs.
Description
- The present Application is a Divisional Application of U.S. patent application Ser. No. 11/666,205, having a §371(c) date of Nov. 16, 2007, which was based on PCT/JP2005/019832 filed on Oct. 21, 2005.
- The present application is based on Japanese Patent Application Nos. 2004-341217 and 2005-034533, the entire contents of which are incorporated herein by reference.
- The present invention relates to a complex resonance circuit including a piezoelectric vibrator such as a quartz resonator, a coil, a capacitor, and an element equivalent to them. The present invention also relates to an oscillation circuit and a filter using the complex resonance circuit.
- A resonance circuit including a coil, a capacitor, and a circuit element equivalent to them is used in various electronic circuits. The resonance circuit is often required to have a resonance frequency controlling function. A resonance frequency of the resonance circuit is typically controlled by changing either one or both of an inductance value of the coil and a capacity (capacitance) value of the capacitor. As one of many important electric circuits utilizing a resonance behavior of the resonance circuit, an oscillation circuit and a filter have been known. The oscillation circuit and the filter are electronic parts indispensable for operating, for example, a portable telephone and various communication apparatuses. In addition, the oscillation circuit and the filter are often required to have an oscillation frequency controlling function and a frequency characteristic (a passband frequency characteristic and a stopband frequency characteristic), respectively.
- The oscillation circuit and the filter are typically provided with a piezoelectric vibrator. This is because fluctuations in a resonance vibration frequency of the piezoelectric vibrator due to aging and ambient temperature variation are relatively small in comparison with other electronic parts. In addition, the piezoelectric vibrator exhibits a excellent short-term stability of the frequency, so that the piezoelectric vibrator is indispensable for operating the oscillation circuit and using electronic devices. A piezoelectric property of a piezoelectric material and a resonance frequency characteristic of the piezoelectric vibrator are extremely useful for the filter too.
- A voltage-controlled piezoelectric oscillation circuit is largely employed as a TCXO (temperature compensated crystal oscillator) for controlling a reference frequency of a portable telephone and a timing-recovering element of a digital circuit. The voltage-controlled piezoelectric oscillation circuit typically has a frequency controlling function. A frequency of the voltage-controlled piezoelectric oscillation circuit is typically controlled by a variable-reactance element such as a variable-capacitance diode.
- Operation frequencies of a typical piezoelectric vibrator vary in a range from several kHz up to several tenth GHz, and thus the piezoelectric vibrator generates a signal whose frequency is adjusted over such the wide range. Depending on the frequency, vibrational motions of the piezoelectric vibrator are referred to as, for example, a tuning fork vibration, a bending vibration, a longitudinal (extensional) vibration, a face shear vibration, a thickness shear vibration, surface wave vibrations, including a face shear, a coupling mode vibration, and a Stoneley surface wave.
- Recently, piezoelectric resonators referred to as a SMR (Solid Mount Resonator) and a FBAR (Film Bulk Acoustic Resonator) are proposed. A piezoelectric device (see, for example, “Technical Handbook of Surface Acoustic Wave Device” edited by the 150th Committee on Technology of Surface Acoustic Wave Device of Japan Society for the Promotion of Science, published by Ohmsha, Ltd., 1991 and “Technical Handbook of Surface Acoustic Wave Device” edited by the 150th Committee on Technology of Surface Acoustic Wave Device of Japan Society for the Promotion of Science, published by Ohmsha, Ltd., 2004) utilizing a MEMS (Micro Electro Mechanical System) technology is also proposed. A new type resonator having interleaved electrodes so as to excite Lamb waves of a high frequency (see, for example, Japanese Patent No. 3400165) is also proposed.
- However, low electric power consumption and miniaturization of the oscillation circuit are prevented by the variable-capacitance diode for controlling a frequency thereof.
- For the sake of expanding a variable-frequency range of the oscillation circuit, it is required to increase a variation width of the capacitance value of the variable-capacitance diode. However, the variation width of the variable-capacitance diode depends on a variation width of an applied voltage thereon, thus it is necessary to increase the applied voltage. A requirement for expanding the variable-frequency range conflicts to a requirement for decreasing the applied voltage of the oscillation circuit. Therefore, both of lowering a power supply voltage effective for low power consumption and an IC integration for miniaturization are not compossible.
- For the purpose of decreasing power supply voltage, a super-cascade type variable-capacitance diode having a large variation width of a capacitance value is used as the variable-capacity diode. In a present production-line, the variable-capacitance diode of this type together with other circuit parts can not be integrated into an IC device for the sake of miniaturization. Therefore, there is no other choice to product an oscillation circuit by assembling the variable-capacitance diode as an individual circuit part.
- Moreover, a mean of precisely controlling a frequency over the wide rage is useful in not only an oscillation circuit but also a filter and various resonance circuits. A new frequency controlling mean replaced by variable-capacitance diode is demanded.
- The present invention is directed to solving the problems described above and provides a resonance circuit that can eliminate a variable-reactance element and a variable-inductance element, both of which are utilized in a typical resonance circuit, and also can control an oscillation frequency of a piezoelectric resonator and a frequency characteristic of a filter. The present invention also provides an oscillation circuit and a filter using the resonance circuit. The present invention also provides a complex resonance circuit including a piezoelectric vibrator whose frequency can be adjusted over a wide rage beyond a limitation of a variable-frequency width. The variable-frequency is dependent upon vibrational motion of the piezoelectric vibrator.
- According to a first aspect of the present invention, there is provided a complex resonance circuit comprising at least two resonance elements having different resonance frequencies and an electric power supply circuit for supplying an electric power to the resonance elements at a variable division ratio. The electric power supply circuit includes two electric power supplying paths respectively connected to the two resonance elements and two variable attenuators or two variable gain amplifiers, each of which is inserted into each of said electric power supplying paths.
- According to a second aspect of the present invention, there is provided a piezoelectric vibration device comprising single piezoelectric substrate, at least three electrode pairs formed on said substrate, and two external connection terminals pairs. The three electrode pairs are connected to the two pairs of external connection terminals so that two different vibration modes individually appear at the external connection terminals.
- According to a third aspect of the present invention, there is provided an oscillation circuit comprising an amplifier, and a feedback part for forming a feedback path connecting across an output end of the amplifier and an input end of the amplifier. The feedback part has a positive feedback path connecting across said output end and said input end and a negative feedback path connecting across said output end and said input end. The negative feedback path which is independent of the positive feedback path has at least two resonance elements having different resonance frequencies and an electric power supply circuit for supplying an electric power supplied from said output end to said resonance elements at a variable division ratio.
- The complex resonance circuit of the present invention has a property that an antiresonance frequency thereof can be adjusted by independently changing voltages or currents for exciting vibrations of the resonance elements. An oscillation circuit and a filter utilizing the property of the complex resonance circuit are configured can be operated on the basis of a new frequency controlling method which has not been conventionally known. The present invention opens the way for realizing a frequency controlling method around at an antiresonance frequency and configuring an oscillation circuit utilizing the frequency controlling method. The frequency controlling method has not been turned into actual utilization since a high impedance is accompanied.
- A piezoelectric device has a plurality of electrodes which are formed on a piezoelectric substrate such as a quartz substrate known as a MCF (Monolithic Crystal Filter). By disposing and connecting the plurality of electrodes so that a plurality of natural vibration modes are generated, an antiresonace frequency appears between resonance frequencies. The disposition and connection of the electrodes are basically different from a conventional technique. The complex resonance circuit of the present invention utilizes a physical property that the antiresonance frequency can vary in response to a ratio of relative output levels of high-frequency signals flowing to the resonance circuits. The complex resonance circuit of the present invention can eliminate a variable-reactance element such as a variable-capacitance diode indispensable for controlling an oscillation frequency characteristic and a filter frequency characteristic, and therefore, is suitable for decreasing voltage applied thereto and lowering electric current consumption.
- Impedances of the filter and the oscillation circuit of the present invention are so high, thus reducing the effectiveness of a resistance component of a peripheral circuitry and exhibiting a high Q-value and an excellent characteristic in a short-term stabilization of an oscillation frequency. The filter of the present invention can exhibit a significant rapid damping characteristic, and in addition, an adjustable-frequency characteristic.
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FIG. 1A is a schematic plan view showing a first embodiment of a complex resonance circuit according to the present invention; -
FIG. 1B is a schematic side view showing the first embodiment of the complex resonance circuit according to the present invention; -
FIG. 2A is a schematic drawing showing a vibration displacement distribution of the complex resonance circuit according to the present invention in a natural vibration mode; -
FIG. 2B is a schematic drawing showing a vibration displacement distribution of the complex resonance circuit according to the present invention in a natural vibration mode; -
FIG. 2C is a schematic drawing showing a vibration displacement distribution of the complex resonance circuit according to the present invention in a natural vibration mode; -
FIG. 2D is a schematic drawing showing a vibration displacement distribution of the complex resonance circuit according to the present invention in a natural vibration mode; -
FIG. 2E is a schematic drawing showing a vibration displacement distribution of the complex resonance circuit according to the present invention in a natural vibration mode; -
FIG. 2F is a schematic drawing showing a vibration displacement distribution of the complex resonance circuit according to the present invention in a natural vibration mode; -
FIG. 3 is a schematic circuit diagram showing a measuring circuit for measuring a frequency characteristic of the complex resonance circuit according to the present invention; -
FIG. 4 is a graph showing frequency characteristics for the first embodiment of the complex resonance circuit according to the present invention; -
FIG. 5 is a graph showing frequency characteristics for the first embodiment of the complex resonance circuit according to the present invention; -
FIG. 6A is a graph showing frequency characteristics for the first embodiment of the complex resonance circuit according to the present invention; -
FIG. 6B is a graph showing frequency characteristics for the first embodiment of the complex resonance circuit according to the present invention; -
FIG. 6C is a graph showing frequency characteristics for the first embodiment of the complex resonance circuit according to the present invention; -
FIG. 7 is a graph showing experimental frequency characteristics for the first embodiment of the complex resonance circuit according to the present invention; -
FIG. 8A is a schematic circuit diagram showing an equivalent circuit representing the measuring circuit ofFIG. 3 ; -
FIG. 8B is a schematic circuit diagram showing an equivalent circuit representing the complex resonance circuit according to the present invention; -
FIG. 8C is a schematic circuit diagram showing an equivalent circuit representing the complex resonance circuit according to the present invention; -
FIG. 8D is a schematic circuit diagram showing an equivalent circuit representing the complex resonance circuit according to the present invention; -
FIG. 9 is a schematic plan view showing a second variation of the first embodiment of the complex resonance circuit according to the present invention; -
FIG. 10 is a schematic plan view showing a third variation of the first embodiment of the complex resonance circuit according to the present invention; -
FIG. 11A is a schematic plan view showing a second embodiment of the complex resonance circuit according to the present invention; -
FIG. 11B is a schematic plan view showing a first variation of the second embodiment of the complex resonance circuit according to the present invention; -
FIG. 12A is a schematic side view showing a second variation of the second embodiment of the complex resonance circuit according to the present invention; -
FIG. 12B is a schematic plan view showing the second variation of the second embodiment of the complex resonance circuit according to the present invention; -
FIG. 12C is a schematic plan view showing the second variation of the second embodiment of the complex resonance circuit according to the present invention; -
FIG. 13A is a schematic perspective view showing a third embodiment of the complex resonance circuit according to the present invention; -
FIG. 13B is a schematic cross-sectional view showing the third embodiment taken along A-A′ line ofFIG. 13A ; -
FIG. 13C is a schematic view showing four electrodes of an upper part of a twin-tuning fork structure of the third embodiment; -
FIG. 13D is a schematic view showing eight electrodes of a lower part of the twin-tuning fork structure of the third embodiment; -
FIG. 13E is a schematic drawing showing a vibration displacement of the upper part of the twin-tuning fork structure of the third embodiment; -
FIG. 13F is a schematic drawing showing a vibration displacement of the lower part of the twin-tuning fork structure of the third embodiment; -
FIG. 14A is a schematic circuit diagram showing a first embodiment of a oscillation circuit according to the present invention; -
FIG. 14B is a schematic circuit diagram showing a variation of the first embodiment of the oscillation circuit according to the present invention; -
FIG. 15 is a graph showing frequency characteristic curve for the first embodiment of the oscillation circuit according to the present invention; -
FIG. 16 is a schematic circuit diagram showing a second embodiment of the oscillation circuit according to the present invention; -
FIG. 17A is a schematic circuit diagram showing a first embodiment of a filter using the complex resonance circuit according to the present invention; -
FIG. 17B is a schematic circuit diagram showing a second embodiment of a filter using the complex resonance circuit according to the present invention; -
FIG. 18 is a schematic circuit diagram showing a conventional double-mode filter; -
FIG. 19A is a schematic drawing showing a vibration displacement distribution of the conventional double-mode filter ofFIG. 18 in a natural vibration mode. -
FIG. 19B is a schematic drawing showing a vibration displacement distribution of the conventional double-mode filter ofFIG. 18 in a natural vibration mode. -
FIG. 20 is a graph showing experimental frequency characteristics for a variation of the first embodiment of the complex resonance circuit according to the present invention; -
FIG. 21A is a schematic circuit diagram showing an equivalent circuit representing the complex resonance circuit according to the present invention; -
FIG. 21B is a schematic circuit diagram showing an equivalent circuit representing the complex resonance circuit according to the present invention; -
FIG. 21C is a schematic circuit diagram showing an equivalent circuit representing the complex resonance circuit according to the present invention; -
FIG. 22A is a schematic circuit diagram showing a third embodiment of the oscillation circuit according to the present invention for cancelling parallel capacities; -
FIG. 22B is a schematic circuit diagram showing an equivalent circuit representing the third embodiment of the oscillation circuit according to the present invention for cancelling parallel capacities; -
FIG. 22C is a schematic circuit diagram showing a variation of the third embodiment of the oscillation circuit according to the present invention for cancelling parallel capacities; -
FIG. 23 is a graph showing experimental frequency characteristics for the third embodiment of the oscillation circuit according to the present invention; -
FIG. 24A is a schematic circuit diagram showing an equivalent circuit representing the equivalent circuit ofFIG. 22B ; -
FIG. 24B is a schematic circuit diagram showing an equivalent circuit representing the third embodiment of the oscillation circuit according to the present invention for cancelling parallel capacities; -
FIG. 25 is a schematic circuit diagram showing a fourth embodiment of the oscillation circuit according to the present invention; -
FIG. 26 is a graph showing experimental frequency characteristics for fourth embodiment of the oscillation circuit according to the present invention; -
FIG. 27A is a schematic circuit diagram of an equivalent circuit representing the fourth embodiment ofFIG. 25 ; -
FIG. 27B is a schematic circuit diagram of an equivalent circuit representing the fourth embodiment ofFIG. 25 ; -
FIG. 27C a circuit diagram of an equivalent circuit representing the fourth embodiment ofFIG. 25 ; and -
FIG. 28 is a schematic circuit diagram showing a fifth embodiment of the oscillation circuit according to the present invention. - Embodiments of the present invention will now be described in detail.
- It is well-known that a piezoelectric device such as a piezoelectric vibrator typically has a large number of natural vibration modes. The natural vibration modes can be classified into a number of mode types. Natural vibration modes having a similar vibration characteristic belong to one of the mode groups. On the basis of the vibration characteristic, the mode groups are referred to as, for example, a bending vibration (including a tuning fork vibration), a longitudinal (extensional) vibration, a face shearing vibration, a width-extensional Vibration, a thickness shearing vibration, a thickness longitudinal vibration, a Rayleigh surface wave vibration, a Leakey surface wave vibration, a shear horizontal surface wave vibration, a SMR vibration, and a Stoneley surface wave vibration.
- A piezoelectric device such as a piezoelectric vibrator utilizing a selected natural vibration mode group is referred to as a “structural device”. Thus, once a structure of, a shape of, and a size of the piezoelectric device are defined, a vibration characteristic of the natural vibration mode can be uniformly described on a dominant conception as is well known even if any materials (piezoelectric material and electrode material) will be used for the piezoelectric device.
- A large number of natural vibration modes belonging to the same mode group are referred to as “group natural vibration mode” or “natural vibration mode group”. The term “order of mode” is utilized for individually identifying the natural vibration modes of the same groups. The order of mode is also referred to as an “harmonic overtone order” and an “inharmonic overtone order”.
- The complex resonator of the present invention including a piezoelectric material utilizes at least two natural vibration modes selected from one of natural vibration mode groups. The at least two natural vibration modes correspond to at least two order of mode. Embodiments of the present invention will be described with reference to order of the natural vibration mode.
- A piezoelectric device such as a piezoelectric vibrator in which both of a natural vibration mode group and its order are selected is a “structural device”. Once a structure of, a shape of, a size of, and a material of the piezoelectric device are defined, a vibrational characteristic of the natural vibration mode can be defined. The piezoelectric device can be universally determined on a dominant conception as is well known, even if any materials (piezoelectric material and electrode material) will be used for the piezoelectric device. If a lowest-order mode of a fundamental wave is selected in a thickness shearing vibration (a natural vibration mode group is selected), a structure and a shape of the piezoelectric vibrator will be completely defined.
- If another order of the vibration mode is selected, the shape of the piezoelectric vibrator will be modified, but the structural concept will not be modified. Thus, the piezoelectric device whose structure is modified is also uniformly defined on a generic concept as is well known. Even if, for example, a thickness shearing vibration mode is selected and then a lowest-order of a fundamental wave is replaced by a highest-order of a fundamental wave, the corresponding structure of the piezoelectric vibrator will be completely defined. Therefore, a structure of the piezoelectric device may be defined on the basis of the corresponding one natural vibration mode group.
- The present invention can utilize all natural vibration mode groups. In other words, the present invention can be defined by a dominant conception where a technical field individually defined by a structure of a piezoelectric vibrator is included. In order to describe that the present invention utilizes all natural vibration mode groups, three embodiments of the complex resonance circuit according to the present invention are firstly described. The first to third embodiments of the complex resonance circuit according to the present invention utilizes a thickness shearing vibration, a Rayleigh surface wave vibration, and a bending vibration, respectively. Then, the dominant conception utilizing natural vibration modes belonging to all natural vibration mode groups will be described.
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FIG. 1A is a schematic plan view showing a first embodiment of a complex resonance circuit according to the present invention.FIG. 1B is a schematic side view showing the first embodiment of the complex resonance circuit according to the present invention. The complex resonance circuit utilizes a thickness shearing vibration of a piezoelectric substrate. A plurality ofelectrodes 1 to 8 are formed on a piezoelectric substrate X1. A piezoelectric device typically has multiple natural vibration modes. A couple of electrodes are connected to the piezoelectric device, and thus some natural vibration modes selected among the multiple natural vibration modes can be induced at the same time by applying a voltage across the electrode. For the sake of selecting a predetermined natural vibration mode, symmetries of and shapes of the electrodes may be appropriately selected. In addition, relative distances between the electrodes and the piezoelectric substrate, and asymmetry of a polarity of a applied signal etc. may be appropriately selected. - The first embodiment of the complex resonance circuit according to the present invention, in which the piezoelectric substrate formed from a piezoelectric material (quartz substrate) is utilized, is also referred to as a “complex resonator”. A principle of the present invention, which will be described in reference to the following drawings, is not limited to the embodiments. The complex resonance circuit according to the present invention includes a complex resonance circuit having other piezoelectric materials such as a ceramic. The complex resonance circuit may be configured by at least one strip line element.
- As shown in
FIGS. 1A and 1B , a complex resonator Re1 includes, afirst electrode 1, asecond electrode 2, athird electrode 3, and afourth electrode 4 adjacently formed on a front surface of the disciform quartz piezoelectric substrate X1. Thefirst electrode 1, thesecond electrode 2, thethird electrode 3, and thefourth electrode 4 face to each other. The complex resonator Re1 further includes afifth electrode 5, asixth electrode 6, aseventh electrode 7, and aneighth electrode 8 formed on a rear surface of the piezoelectric substrate X1. The fifth, sixth, seventh, andeighth electrodes fourth electrodes FIG. 1A , the electrodes formed on the rear surface of the piezoelectric substrate X1 are denoted by numerals (5), (6), (7), and (8) and the lead wires etc. formed on the rear surface are denoted by dotted lines. - The connection between the lead wires and the electrodes will now be described. As shown in
FIG. 1A , the electrodes are connected to each other via the lead wires. Both of thefirst electrode 1 and thesecond electrode 2 are connected to a first external terminal T1. Both of thefifth electrode 5 and thesixth electrode 6 are connected to a second external terminal T2. Both of thethird electrode 3 and theeighth electrode 8 are connected to a third external terminal T3. Both of thefourth electrode 4 and theseventh electrode 7 are connected to a fourth external terminal T4. - In the first embodiment of the present invention, the complex resonator includes at least two electrode pairs formed on the front surface of the piezoelectric substrate and at least two electrode pairs formed on the rear surface so that each of the electrode pairs is independently piezoelectrically coupled to the piezoelectric substrate. For the purpose of suppressing spurious vibration excitations, it is preferable that the four electrode pairs are formed on principal surfaces of the piezoelectric substrate so as to be substantially symmetrical to each other in the horizontal and vertical directions of principal surfaces of the substrate. As shown in
FIG. 1A , it is not indispensably required that the electrodes are symmetric with respect to a center point of the piezoelectric substrate. - Sizes of the electrodes of the first embodiment will now be specifically described. In
FIGS. 1A and 1B , the piezoelectric plate X1, which is an AT-cur circular quartz substrate having a diameter of about 8 mm, excites a resonance vibration frequency of about 10 MHz. The electrodes have a square shape having 1.5 mm on one side and are separated from each other by a distance of about 0.3 mm. The electrodes are arranged in the middle of the piezoelectric plate X1 so as to be substantially symmetric to each other in the vertical and horizontal directions of the piezoelectric plate X1. Each of the lead wires has a width of about 0.3 mm. In a circumferential portion of the piezoelectric plate X1, the lead wires are connected to the external connection terminals T via a conductive adhesive etc. The electrodes and the lead wires, which are formed from an Ag film with a 150 nm thickness, are formed by evaporating under vacuum. - The complex resonator Re1 of
FIG. 1A is characterized by the arrangement of the electrodes and the interconnections between the electrodes. Both of thefirst electrode 1 and thesecond electrode 2, which are formed on the front surface of the piezoelectric substrate X1, are connected to the external terminal T1. Both of thefifth electrode 5 and thesixth electrode 6, which are formed on the rear surface of the piezoelectric substrate X1, are connected to the terminal T2. Both of thethird electrode 3 and theeighth electrode 8 which is not opposed to thethird electrode 3 is connected to the third terminal T3. Both of thefourth electrode 4 and theseventh electrode 7 which is not opposed to thefourth electrode 4 are connected to the fourth terminal T4. - In consideration of differences between the vibration modes which respectively appear to external electrode pairs, the external terminal pairs are distinctively defined as a positive terminal pair and a negative terminal pair, respectively. For instance, in the case that an external terminal pair of T1 and T2 are defined as a positive terminal pair, both of the
first electrode 1 and thesecond electrode 2 are connected to the terminal T1 and both of thefifth electrode 5 and thesixth electrode 6 are connected to the terminal T2. In other wards, two electrodes formed on the front surface of the piezoelectric substrate and two electrodes formed on the rear surface of the piezoelectric substrate are connected to the external electrode pair of T1 and T2, respectively. - On the other hand, an external terminal pair of T3 and T4, across which a vibration mode different from the positive terminal pair appears, is distinctively defined as a negative terminal pair. Both of the
third electrode 3 and theeighth electrode 8 are connected to the terminal T3 which is one terminal of the negative terminal pair. Both of thefourth electrode 4 and theseventh electrode 7 are connected to terminal T4 which is the other terminal of the negative terminal pair. In other wards, two electrodes respectively formed on the different surfaces of the piezoelectric substrate and two electrodes formed on the different surfaces of the piezoelectric substrate are connected to the external electrode pair of T3 and T4, respectively. The connection of the electrodes to the positive terminal pair is defined as a positive polarity connection. The connection of the electrodes to the negative terminal pair is defined as a negative polarity connection whose polarity is opposite to the positive polarity connection. - An electrode structure and an operation of the first embodiment will now be described for clarifying a basic idea of the present invention in comparison with a conventional piezoelectric device.
- A double-mode piezoelectric filter having, for example, an electrode structure shown in
FIG. 18 , is conventionally known. Two electrode pairs of 21 (22) and 23 (24) are opposite to each other with respect to a piezoelectric substrate X1. The electrodes 21 (22) and 23 (24) are slightly separated by a distance. Theelectrodes external electrodes electrodes external electrodes FIG. 19A and the other of which is an asymmetrical mode as shown inFIG. 19B . In the asymmetrical mode shown inFIG. 19B , the piezoelectric substrate asymmetrically vibrates in the vertical direction. As shown inFIG. 18 , the number of the electrodes formed on piezoelectric filter is basically four. The number of electrodes is dependent on operation status of the piezoelectric filter. The number of electrodes is three in the case that two electrodes formed on one surface of the piezoelectric substrate are connected to one as a common electrode. - Meanwhile, the first embodiment of the complex resonator Re1 shown in
FIG. 1B includes eight electrodes, four of which are formed on the front surface of the piezoelectric substrate and four of which are formed on the rear surface reverse to the front surface. (As will be described later, in the case of sharing the electrodes, a complex resonator includes six electrodes, three of which are formed on a front surface and three of which are formed on a rear surface) It is understood from the comparison of both electrode structures that the complex resonator of the present invention is basically different from the conventional piezoelectric device. - Furthermore, the complex resonator of the present invention is completely different from the conventional piezoelectric filter in a point of its performance and operation. The conventional piezoelectric filter utilizes some natural vibration modes selected among multiple natural vibration modes and the natural vibration modes can be excited at the same time. The conventional piezoelectric filter has a filtering function by utilizing plural natural vibration modes. The plural natural vibration modes are uniquely determined from the electrode structure. On the other hand, the complex resonator of the present invention includes at least one electrode pair or two electrode pairs and generates different natural vibration modes at the same time. As will be described in later, the complex resonator of the present invention utilizes a physical phenomenon not known conventionally.
- As shown in
FIG. 1B , the complex resonator Re1 has the piezoelectric substrate, on one principal surface of which the four electrodes are formed and on the other principal surface of which the four electrodes are formed. A distance between the electrodes, which is configured to be 0.3 mm, is small in comparison with the size of the electrode, so that the piezoelectric substrate and all electrode surfaces integrally vibrate. In addition, the electrodes are arranged on the piezoelectric substrate on the basis of polarities. Thus, a plurality of natural vibration modes appear as shown inFIGS. 2A to 2F . Each ofFIGS. 2A to 2F conceptually illustrates a contour map of vibration amplitude of a natural vibration mode so as to represent a vibration displacement in two-dimensional. Although sizes of circles and ellipses shown inFIGS. 2A to 2F are schematically illustrated, piezoelectric substrates (quartz plates) X1 are illustrated so as to have the same diameter and be arranged in the same direction. - Amplitude of vibration displacement in a marginal portion of a quartz plate is typically zero. Each of
FIGS. 2A to 2F indicates that vibration displacement increases in amplitude as the number of contour lines increase. For instance, inFIG. 2A , an absolute value of the vibration displacement has the maximum at a center of the piezoelectric substrate (quartz plate) X1. Directions of the vibration displacement are denoted by solid and dotted lines of each ofFIGS. 2A to 2F , whose vibration directions are reverse to each other. - In the first embodiment of the complex resonance circuit shown in
FIG. 1A , each of the electrodes is configured so as to have the same size. These electrodes are arranged on the quartz plate so as to be substantially symmetric with respect to the piezoelectric substrate X1 in the vertical and horizontal directions. As described, the polarities of the electrodes are configured in the following way. As shown inFIG. 1A , the electrode pair of the first electrode and the second electrode, which pair is arranged on an upper part of the front surface of the piezoelectric substrate X1, has the same polarity as the terminal pair of the fifth electrode and the sixth electrode, which pair is arranged on the upper part of the rear surface of the piezoelectric substrate X1. The terminal pair of the third electrode and the eighth electrodes which are respectively arranged on a lower part of the front and rear surface of the piezoelectric substrate X1 shownFIG. 1A , has the same polarity as the terminal pair of the seventh electrode and the fourth electrodes which are respectively arranged on the lower part of the front and rear surface. The former two electrodes pairs have the same polarity opposed to that of the latter two electrode pairs. Therefore, two natural vibration modes ofFIGS. 2A and 2B are efficiently excited by applying a high-frequency electric current across the external terminals T1 and T2. In addition, two natural vibration modes shown inFIGS. 2C and 2D are efficiently excited by applying a high-frequency electric current across the external terminals T3 and T4. - The first and
second electrodes sixth electrodes second electrodes FIG. 2B is excited.FIG. 2A shows that the piezoelectric substrate X1 vibrates at a vibration displacement a1 denoted by the solid line whose direction is a forward direction and also shows that the piezoelectric substrate X1 vibrates symmetrically in the vertical and horizontal directions. The counter map ofFIG. 2B shows that the upper portion of the piezoelectric substrate X1 vibrates at a vibration displacement a1 denoted by solid line whose direction is a forward direction and also shows that the lower portion of the piezoelectric substrate X1 vibrates at a vibration displacement a2 denoted by the dotted line whose direction is reverse to the forward direction.FIG. 2B shows that the vibration of the piezoelectric substrate X1 is substantially symmetric in the horizontal direction and substantially asymmetric in the vertical direction. - Natural vibration modes shown in
FIGS. 2C and 2D are characterized by vibration displacements which are substantially asymmetric in the horizontal direction. The vibration displacement ofFIG. 2C is substantially symmetric in the vertical direction and the vibration displacement ofFIG. 2D is substantially asymmetric in the vertical direction. These natural vibration modes have corresponding natural vibration frequencies. In similar to a conventional piezoelectric vibrator, the absolute values and the relative values (a frequency difference between two natural vibration frequencies) of these natural vibration frequencies are dependent upon material constants, shapes, and sizes of the piezoelectric substrate and the electrodes constituting the piezoelectric vibrator. - Frequency characteristics for the complex resonator Re1 of the first embodiment are measured via the external terminals with a measuring circuit shown in
FIG. 3 . The measuring circuit includes a high-frequency signal generator SG for supplying an input signal to the external terminals T1 and T3 of the complex resonator Re1 show inFIG. 1A via attenuators ATT1 and ATT2. The measuring circuit further includes a level measuring instrument L1 for measuring an output signal level from the external terminals T2 and T4. The complex resonator Re1, which is the quartz resonator of the first embodiment shown inFIG. 1A , is schematically illustrated inFIG. 3 . - A measurement result observed with the level measuring instrument L1 is shown in
FIG. 4 .FIG. 4 is a graph showing frequency characteristic curves for the first embodiment of the complex resonator according to the present invention. The frequency characteristic curve b1 is observed by varying a frequency of the input signal supplied to the complex resonator Re1 under a configuration condition that an attenuation value of the attenuator ATT1 ofFIG. 3 is 0 dB, an attenuation value of the attenuator ATT2 is 100 dB, and an amplitude of the input signal supplied from SG is constant. Under such the configuration condition, an output signal observed by the level measuring instrument L1 is dominated by the input signal from the attenuator ATT1. This behavior results from influences of the natural vibration modes respectively appearing to the first andsecond electrodes sixth electrodes - Under such the configuration, a frequency characteristic curve b1 denoted by a solid line of
FIG. 4 is observed. As shown inFIG. 4 , the frequency characteristic curve b1 has two peaks at frequencies f1=9.82272 MHz and f2=9.85290 MHz which correspond to resonance frequencies. - Next, when the attenuation value of the attenuator ATT1 is increased from 10 to 20 dB, an frequency characteristic curve (not shown) similar to the frequency characteristic curve b1 having two peaks at f1 and f2 is observed. However, the intensity of the frequency characteristic curve entirely decreases and the frequency characteristic curve shifts in a direction toward to lower output level (vertical axis) in parallel, resulting from the increase in the attenuation value of the attenuator ATT1. Frequencies of the two peaks at f1 and f2 ascribed to resonance frequencies do not substantially shift. It is considered that the two frequencies f1 and f2 correspond to the natural vibration frequencies causing the vibration displacements of
FIGS. 2A and 2B , respectively. - Next, a measurement is performed while varying a frequency of the input signal supplied to the complex resonator Re1 under a configuration condition that an attenuation of the attenuator ATT1 is 100 dB, an attenuation of the attenuator ATT2 is 0 dB, and an amplitude of the input signal supplied from SG is constant. Under such the configuration condition, a frequency characteristic curve b2 denoted by a dotted line of
FIG. 4 is observed. The frequency characteristic curve b2 has two peaks at frequencies f3=9.86763 MHz and f4=9.89735 MHz f3 corresponding to resonance frequencies. - Next, when the attenuation value of the attenuator ATT2 is increased from 10 to 20 dB, an frequency characteristic curve (not shown) similar to the frequency characteristic curve b2 having two peaks at f3 and f4 is observed. However, the intensity of the frequency characteristic curve entirely decreases and the frequency characteristic curve shifts in a direction toward to lower output level (vertical axis) in parallel, resulting from the increase in the attenuation value of the attenuator ATT2. Frequencies of the two peaks at f3 and f4 ascribed to resonance frequencies do not substantially shift. It is considered that the two frequencies f3 and f4 correspond to the natural vibration frequencies causing the vibration displacements of
FIGS. 2C and 2D , respectively. - The above-described measurement result will now be summarized as follows. Under such the configuration condition that the attenuation value of the attenuator ATT1 is 0 dB and the attenuation value of the attenuator ATT2 is 100 dB, the frequency characteristic curve b1 having the two peaks at the frequencies f1 and f2 is observed. Under such the configuration condition that the attenuation value of the attenuator ATT1 is 100 dB and the attenuation value of the attenuator ATT2 is 0 dB, the frequency characteristic curve b2 having the two peaks at the frequencies f3 and f4 is observed.
- Next, under a configuration condition that both attenuation values of the attenuator ATT1 and the attenuator ATT2 are 0 dB, a frequency characteristic curve b3 of
FIG. 5 is observed. It is apparent from the frequency characteristic curve b3 that a dip corresponding to an antiresonance frequency fp appears between two resonance frequencies f2 and f3. - A frequency characteristic of the resonance circuit according to the present invention will now be described. An antiresonance frequency fp appearing between resonance frequencies f2 and f3 can be adjusted by changing a difference in attenuation values between the attenuators ATT1 and ATT2 of
FIG. 3 . -
FIGS. 6A to 6C are graphs showing frequency characteristic curves for the first embodiment of the complex resonance circuit according to the present invention, which curves are around between resonance frequencies f2 and f3.FIGS. 6A to 6C show that an antiresonance frequency fp can be adjusted between two resonance frequencies f2 and f3 by changing a difference in attenuation values between the attenuators ATT1 and ATT2. -
FIG. 6A is a graph of a frequency characteristic curve b4 for the first embodiment, which curve is observed under the configuration that the attenuators ATT1 and ATT2 have the same attenuation values. As shown inFIG. 6A , the observed frequency characteristic curve b4 has a dip corresponding to an antiresonance frequency fp at a substantial midpoint of frequencies f2 and f3.FIG. 6B is a graph of a frequency characteristic curve b4 for the first embodiment, which curve is observed under the configuration that an attenuation value of the attenuator ATT2 is larger than that of the attenuator ATT1. As shown inFIG. 6B , the observed frequency characteristic curve b4 has a dip corresponding to an antiresonance frequency fp between frequencies f2 and f3, and in particular, close to f3.FIG. 6C is a graph of a frequency characteristic curve b4 for the first embodiment, which curve is observed under the configuration that an attenuation value of the attenuator ATT1 is larger that that of the attenuator ATT2. As shown inFIG. 6C , the observed frequency characteristic curve b4 has a dip corresponding to an antiresonance frequency fp between frequencies f2 and f3, and in particular, close to f2. - As is clear from the experimental results, it is understood that the antiresonance frequency fp can be varied by continuously changing the difference in attenuation values between the attenuators ATT1 and ATT2.
-
FIG. 7 is a graph showing antiresonance frequency characteristics for the first embodiment. The vertical axis ofFIG. 7 corresponds to a normalized antiresonance frequency value which is normalized by configuring that a lower frequency f2 is 0% and a higher frequency f3 is 100%. The horizontal axis corresponds a relative value between attenuation values of the attenuators ATT1 and ATT2. - The zero-point on the horizontal axis corresponds to the case that both of the attenuation values are equal to each other. The negative direction along the horizontal axis corresponds to an increase of the attenuation value of the attenuator ATT1 at the time when the attenuation value of the attenuator ATT2 is 0 dB. The attenuator ATT1 is connected to the external terminals T1 and T2 to which a lower natural vibration mode appears. The attenuator ATT2 is connected to the external terminals T3 and T4 to which a higher natural vibration mode appears. The positive direction along the horizontal axis corresponds to an increase of the attenuation value of the attenuator ATT2 at the time when the attenuation value of the attenuator ATT1 is 0 dB.
- It is to be noted that the measuring circuit of
FIG. 3 further includes an impedance matching type power divider (not shown) connected across a high frequency signal generator SG and the two attenuators ATT1 and ATT2. It is conventionally known to utilize the impedance matching type power divide. For the sake of simplifying a relation between the attenuation values of the attenuators ATT1 and ATT2 and applied voltages on the external terminals T1 and T3, the impedance matching type power divider is not shown inFIG. 3 . - It is understood from
FIG. 7 that the value of antiresonance frequency fp can be widely varied over the wide rage up to 35% which value corresponds to the difference between the frequencies f2 and f3 and an absolute value of 500 ppm. - The first embodiment of the complex resonance circuit according to the present invention can be modified so that the piezoelectric substrate shown in
FIG. 1A is replaced by two conventional piezoelectric vibrators Q1 and Q2. In a first variation of the first embodiment too, an antiresonance frequency fp can be adjusted by utilizing the conventional piezoelectric vibrators Q1 and Q2. - A frequency variable effect made by two quartz resonators employed as the piezoelectric vibrator will now be described with reference to the circuit of
FIG. 3 . The quartz resonator Re1 ofFIG. 3 is replaced by two quartz resonator. A quartz resonator Q1 is connected across the external terminals T1 and T2 shown inFIG. 3 . A quartz resonator Q2 is connected across external the terminals T3 and T4 shown inFIG. 3 . Resonance frequencies of the two quartz resonators Q1 and Q2 is 9.995200 MHz and 10.005116 MHz, respectively. Each of the quartz resonators Q1 and Q2 is formed from a disciform AT-cut quartz substrate having a diameter of 6.5 mm, on which circular electrodes having a diameter of 3 mm are formed. The circular electrodes are formed by evaporating silver under vacuum. It is configured that a range of a frequency drop plate back frequency is about 70 kHz. The quartz resonators having the electrode are electrically attached to a HC-49/U package with a conductive adhesive, and then the quartz plate are hermetically sealed under dry nitrogen. - Frequency characteristics for the complex resonator including the resonators Q1 and Q2 are observed by the measurement circuit of
FIG. 3 . Two peaks ascribed to the spurious peaks f1 and f4 which are observed in the first embodiment ofFIG. 1A , are not observed. Two peaks corresponding to the resonance frequencies f2 and f3 are observed for the first variation of the first embodiment having the two quartz resonators Q1 and Q2. Therefore, frequency characteristics similar toFIGS. 6A to 6C are observed by the measuring circuit ofFIG. 3 to which the quartz resonators Q1 and Q2 are connected. - In similar to
FIG. 7 , antiresonance frequency characteristics for the first variation of the first embodiment having the two piezoelectric resonators Q1 and Q2 are observed while changing a difference in attenuation values between the attenuator ATT1 and ATT2.FIG. 20 is a graph of antiresonance frequency characteristics for the first variation of the first embodiment having the piezoelectric resonators Q1 and Q2. It is understood fromFIG. 20 that values of the antiresonance frequency fp can be adjusted over a wide rage up to 93.4% of a frequency difference between the resonance frequencies f2 and f3. An absolute value of the maximum normalized antiresonance frequency is 926 ppm. - Even if the two piezoelectric vibrators are separately disposed and connected to a plurality of electrodes, in the case of vibration modes due to an energy trapping effect, the two piezoelectric vibrators can make effects similar to one piezoelectric substrate having two separate portions which are uniformly spaced.
- In
FIG. 7 , the normalized frequency does not reach 50% at 0 dB, that is, under a condition that both attenuation values of the two attenuators are equal to each other. The reason is speculated as follows. As shown inFIG. 3 , the piezoelectric vibrator of the first embodiment has two portions, one of which is connected across the external terminals T1 and T2 and the other of which is connected across the external terminals T3 and T4. Since each of the portions of the piezoelectric vibrator in the complex resonator has a parallel capacity, Q-value (sharpness of the peak resonance) of the piezoelectric vibrator is low. Accompanied by the low Q-value, each of the frequency characteristic curves b1 to b4 ofFIGS. 4 to 6 is horizontally asymmetric in the horizontal axis. The piezoelectric substrate used for the piezoelectric vibrator observed inFIG. 7 excites a thickness shear vibration mode on the AT-cut quartz substrate, so that the capacitance ratio is about 250. Therefore, the asymmetry of the frequency characteristic curves b1 to b4 is originated from such the high capacitance ratio. - The asymmetry of the frequency characteristic curves depends on the piezoelectric substrate used in the complex resonator of the present invention. The asymmetry also depends on a capacitance ratio (or an electromechanical coupling factor) peculiar to the natural vibration modes excited in the piezoelectric substrate. Although the asymmetry decreases as the capacitance ratio decreases, the asymmetry can be reduced by cancelling the parallel capacity of the piezoelectric vibrator.
- For the purpose of cancelling the parallel capacities of the piezoelectric vibrator, the complex resonator according to the present invention may include coils which are respectively connected across T1 and T2 and across T3 and T4. The coil has an inductance value so as to cause a parallel resonance by which the parallel capacity is cancelled. In addition, the complex resonator according to the present invention may utilize a bridge balance method or includes a T-shaped circuit having a condenser and a coil. The bridge balance method or the T-shaped circuit having a condenser and a coil will be described later together with an oscillation circuit.
- As shown in
FIGS. 7 and 20 , in the first embodiment and the first variation of the first embodiment, it is observed that the antiresonance frequency fp is preferably correlated with the difference in attenuation values between the two attenuators. A theoretical analysis of the correlation will now be described with reference toFIG. 21A . - The measuring circuit shown in
FIG. 3 can be replaced by an equivalent circuit shown inFIG. 21A . The high frequency signal generator SG ofFIG. 3 corresponds to an AC power source E and a resistance RS ofFIG. 21A . The level measurement instrument L1 ofFIG. 3 corresponds to a resistance RL ofFIG. 21A . In the case that the complex resonator Re1 ofFIG. 3 corresponds to, for example, the complex resonator ofFIG. 1A , it is understood from the electrode structure and the electrode connection shownFIG. 1A that the complex resonator ofFIG. 1A excites at two natural vibrational modes on the one piezoelectric substrate. This is because that the two natural vibrational modes are orthogonal to each other as shown inFIGS. 2B and 2C . - In the first variation of the first embodiment, the complex resonator Re1 of
FIG. 3 corresponds to the two piezoelectric resonators Q1 and Q2 which are individually connected to the measuring circuit. Thus, the two piezoelectric resonators independently excite different vibrational modes. Thus, the complex resonator Re1 shown inFIG. 3 can be also replaced by two typical equivalent circuits surrounded by a dotted line ofFIG. 21A . Each of the typical equivalent circuits is represented by four equivalent constants. The complex resonator Re1 between the external terminals T1 and T2 ofFIG. 3 corresponds to the equivalent circuit between terminals T1 and T2 shown inFIG. 21A . The complex resonator Re1 between the external terminals T3 and T4 ofFIG. 3 corresponds to the equivalent circuit between terminals T3 and T4 shown inFIG. 21A . The equivalent circuit between the terminals T1 and T2 ofFIG. 21A has a parallel circuit configured by L11, C11, r11, and CO1. L11, C11, r11 are connected in series. The equivalent circuit between the terminals T3 and T4 ofFIG. 21A has a parallel circuit configured by L12, C12, r12, and CO2. L12, C12, r12 are connected in series. An output voltage of the attenuator ATT1 ofFIG. 3 is defined as V1. An output voltage of the attenuator ATT2 ofFIG. 3 is defined as V2. An output voltage of the level measurement instrument L1 ofFIG. 3 is defined as V3 which is a voltage across both ends of the resistance RL. - Furthermore, the equivalent circuit shown in
FIG. 21A can be replaced by an equivalent circuit shown inFIG. 21B . The AC power source E, the resistance RS, the attenuator ATT1, and the attenuator ATT2 ofFIG. 21A can be represented as two AC power sources e1, e2 and two resistances R1, R2 as shownFIG. 21B . Amplitudes of the two AC power sources e1, e2 and values of the resistances R1, R2 are configured so that voltages V1 to V3 at terminals shown inFIG. 21B are equivalent to those ofFIG. 21A . - The complex resonator Re1 of the equivalent circuit of
FIG. 21A is not essentially influenced by two parallel capacities CO1 and CO2, both of which can be canceled as will be described later. Therefore, the equivalent circuit ofFIG. 21B , in which two parallel capacities CO1 and CO2 are disregarded, will be described. - A purpose of analyzing the equivalent circuit of
FIG. 21B is to clarify a dependence of the antiresonance frequency fp in response to the voltages V1 and V2. For this purpose, only a zero-point of a transfer function of the equivalent circuit ofFIG. 21B may be calculated. In other words, a zero-point of an output current IL may be calculated when a resistance RL is adjusted to be zero. If resistances of r11 and r12 of the complex resonator shown inFIG. 21B are assumed to be 0 for the sake of simplicity, the equivalent circuit ofFIG. 21B can be partially replaced by an equivalent circuit shown inFIG. 21C . - The output current IL of the equivalent circuit of
FIG. 21C is calculated by using the voltages V1 and V2 on the basis of the superposition principle. Since a numerator of the transfer function is not zero, a condition under which a denominator of the transfer function becomes 0 is given by the following equation. -
- By dividing both sides of the
equation 1 with a square root of a product of V1 and V2, the following equation is obtained. -
- If an angular frequency ω of the
equation 2 is solved, an antiresonance angular frequency ωp will be obtained. By dividing the antiresonance angular frequency ωp with 2π, the following equation is obtained. -
- The
equation 3 is a frequency equation representing the correlation between the antiresonance frequency fp and the voltages V1, V2. - An equivalent circuit of the complex resonator according to the present invention will be intuitively described.
- In the frequency equation of the
equation 3, four equivalent constants are multiplied by a square root of V1 and V2. Therefore, only in order to intuitively understood the antiresonance frequency fp dependence of the complex resonator in response to the voltages V1 and V2, an equivalent circuit shown inFIG. 8B is intuitive and comprehensible. Similar to the equivalent circuit ofFIG. 8B , the complex resonator can be also represented as equivalent circuits shownFIGS. 8C and 8D - When the measuring circuit of
FIG. 3 is represented as an equivalent circuit shown inFIG. 8A , the complex resonator Re1 ofFIG. 3 is represented as the equivalent circuit ofFIG. 8B . As shown inFIG. 8B , the equivalent circuit is configured by two independent series resonance circuits. When the output voltages of the attenuators ATT1 and ATT2 ofFIG. 3 are given by V1 and V2, respectively, equivalence constants of the series resonance circuits are represented as shown inFIG. 8B . - The equivalent constants of the series resonance circuits of
FIG. 8B are obtained as follows. An equivalent inductance across the external terminals T1 and T2 is expressed as L1×√(V2/V1) (L1 multiplied by a square root of V2/V1). An equivalent capacitance (capacitor) across the external terminals T1 and T2 is expressed as C1×√(V1/V2). In the same way, an equivalence inductance across the external terminals T3 and T4 is expressed as L2×√(V1/V2). An equivalent capacitance (capacitor) across the external terminals T3 and T4 is expressed as C2×√(V2/V1). - Values of the equivalent inductance L1, the equivalent capacitance C1 (capacitor), the equivalent inductance L2, and the equivalent capacitance C2 (capacitor) is given when the output voltage V1 of the attenuator ATT1 is same as the output voltage V2 of the attenuator ATT2.
- In this equivalent circuit, the two series resonance circuits are connected in parallel to each other via the attenuators ATT1 and ATT2. Although two series resonance frequencies of the two series resonance circuits do not depend on the voltages V1 and V2, an antiresonance frequency between these series is varied in response to the voltages V1 and V2. An approximation similar to the
equation 3 is given by the following equation. -
- The
equation 35 is represented as the equivalent circuits shown inFIG. 8B , C, and D. The equivalent circuit shown inFIG. 8B has equivalent constants of two series resonance circuits, which constants vary in response to the voltages V1 and V2. An inductance value of the series resonance circuits is inversely proportional to a capacitance value thereof with respect to the voltage V1 and V2 (If one of the inductance value and the capacitance value increases, the other decreases. A product of the inductance value and the capacitance value is constant). Thus, the series resonance frequencies do not changes, which is in agreement with the above-described measurement results. - The equivalent circuit shown in
FIG. 8C is represented on the basis of ratios of transformations of transformers. Variations of an equivalent resistance R1, a parallel capacitor CO1, an equivalent resistance R2, and a parallel capacitor CO2 are also represented as shown inFIG. 8C . - In the equivalent circuit shown in
FIG. 8D , a circuit which a range of a leakage coupling is represented by ratios φ1, φ2 of transformations of transformers in the case that shapes and arrangements of the electrodes of the complex resonance circuit shown inFIG. 1 are asymmetric is added to the equivalent circuit shown inFIG. 8C . The additional circuit corresponds to a part enclosed by a dotted line ofFIG. 8D . It is understood fromFIG. 8D that a dependence of an antiresonance frequency fp in response to the voltages V1 and V2 is defined even if the ratios are 0.5, in other wards, a “leakage coupling” is about 50%. - As described above, in the complex resonator according to the present invention, the antiresonance frequency can vary in response to amplitudes of voltages or currents respectively supplied to two resonance series circuits, and more accurately, in response to a ratio of amplitudes of voltages or currents respectively supplied to two resonance circuits. If an oscillation circuit is configured by using the complex resonator of the present invention, an output frequency of the oscillation circuit will be controlled by adjusting two voltages supplied thereto. If a filter is configured by using the complex resonator of the present invention, a frequency characteristic of the filter such as a passband frequency and a stopband frequency will be controlled by adjusting two voltages supplied thereto.
- In addition, the complex resonator of the present invention can be controlled its frequency without a variable-reactance element such as a variable-capacitance diode, which is indispensable for a conventional oscillation circuit. Thus, the complex resonator of the present invention is appropriate for an IC integration.
- In the first embodiment, it is described that the antiresonance frequency fp can be equivalently controlled by selecting two natural vibration modes which are excited at natural vibration frequencies adjacent to each other and controlling the vibration modes independently.
- The first embodiment of the present invention may be modified as follows. The electrode structure shown in
FIG. 1A may be replaced by, for example, an electrode structure shown inFIG. 9 . In a second variation of the first embodiment, first and second electrodes formed on a front surface of a piezoelectric substrate are coupled together and fifth and sixth electrodes formed a rear surface are coupled together. The coupled electrodes have the same polarity. - The first embodiment of the present invention may be also modified as follows. A third variation of the first embodiment has an electrode structure in which unnecessary vibrations can be reduced. For reducing the unnecessary vibrations, the electrode structure shown in
FIG. 1A is replaced so that the electrodes ofFIG. 1A is substantially symmetric in the vertical direction. In the electrode structure ofFIG. 1A , the four natural vibration modes shown inFIG. 2A , 2B, 2C, and 2D can be excited. However, only the two natural vibration modes ofFIG. 2B andFIG. 2C are actually utilized in the first embodiment. That is, the natural vibration modes ofFIG. 2A andFIG. 2D are unnecessary. If excitations of the unnecessary natural vibration modes are suppressed, spurious resonance peaks will be reduced. For reducing the unnecessary vibrations, the electrode structure ofFIG. 1A of the first embodiment may be replaced by an electrode structure shown inFIG. 10 . - In the third variation of the first embodiment, a complex resonator Re2 shown in
FIG. 10 includes afirst electrode 11, asecond electrode 12, a third electrode 13, and afourth electrode 14 which are formed on a front surface of a piezoelectric substrate X2 such as a quartz substrate. The third electrode 13 and thefourth electrode 14 are formed between thefirst electrode 11 and thesecond electrode 12. The complex resonator Re2 also includes afifth electrode 15 opposed to the first electrode, asixth electrode 16 opposed to the second electrode, aseventh electrode 17 opposed to the third electrode, and aneighth electrode 18 opposed to the fourth electrode, which electrodes are formed on a rear surface of the piezoelectric substrate. - The first and
second electrodes sixth electrodes sixth electrodes second electrodes fourth electrodes 13, 14, which are formed between the first andsecond electrodes eighth electrodes eighth electrodes fourth electrodes 13, 14, respectively. These electrodes are connected to external terminals, respectively. The first andsecond electrodes sixth electrodes eighth electrodes 13, 18 are connected to a third external terminal T13. The fourth andseventh electrodes - In such the electrode configuration, four electrode pairs are disposed on an upper part, a middle part, and a lower part of the piezoelectric substrate X2. The
electrodes electrodes electrodes electrodes electrodes 13, 17 and theelectrodes electrodes 13 and 14, both of which are formed on the same surface, are electrically connected so that electric potentials thereat are different from each other. Theelectrodes FIGS. 2B and 2D , are not excited. Therefore, the natural vibration modes as shown inFIG. 2A andFIG. 2C , which are independently excited, appear across the external terminals T11 and T12 and across T13 and T14, respectively. Whereby, the third variation of the first embodiment has a frequency variable characteristic similar to the first embodiment, and in addition, has an effect that a spurious characteristic is suppressed since the unnecessary modes are not excited or drastically suppressed. - The third variation of the first embodiment for suppressing excitations of unnecessary natural vibration modes has been described with reference to
FIG. 10 . A fourth variation of the first embodiment having electrodes which are also arranged in symmetric with respect to the vertical direction will now be described with reference toFIG. 10 . Theelectrode 11 formed on the upper part of the front surface of the piezoelectric substrate X2 is divided into two electrodes like the twoelectrodes 13 and 14. Theelectrode 15 formed on the upper part of the rear surface of the piezoelectric substrate X2 is divided into two electrodes like the twoelectrodes electrodes electrodes 13 and 14 and twoelectrodes electrodes 13 and 14 formed on the center part of the front surface are connected to each other as a common electrode. Theelectrodes FIGS. 2A and 2C are excited. Whereby, the fourth variation of the first embodiment has a frequency variable characteristic similar to the first embodiment, and in addition, has an effect that spurious characteristic is suppressed since the unnecessary modes are not excited or drastically suppressed. Connections between the electrodes and external terminals are omitted since they are connected as shownFIG. 10 . - A second embodiment of the complex resonance circuit according to the present invention will now be described. The second embodiment utilizes Rayleigh surface waves as normal vibration modes. As shown in
FIGS. 11A and 11B , the second embodiment has an electrode structure configured by eight interdigital electrode pairs. Similar to a conventional surface wave device, the number of interdigital electrode pairs and the number of bars of the interdigital electrode are increased so that the interdigital electrodes have shapes symmetric to each other. - As shown in
FIG. 11A , aninterdigital electrode 31 having a plurality of parallel, spaced-apart bars is formed on a piezoelectric substrate X3. Theinterdigital electrode 31 is connected to abus bar part 32. Aninterdigital electrode 33 is formed on the piezoelectric substrate X3 so as to be interdigital with theinterdigital electrode 31. Theinterdigital electrode 33 is connected to abus bar part 34. Thebus bar parts bus bar parts bus bar parts - The plurality of bars of the first interdigital electrode pair formed on an upper part of the piezoelectric substrate X3 is connected so that a periodical electrical potential in phase is applied thereto in the horizontal direction. The plurality of bars of the second interdigital electrode pair formed on an lower part of the piezoelectric substrate X3 is connected so that a periodical electrical potential is applied thereto and a phase of the electrical potential are reverse with respect to a center part thereof. More specifically, in the center of the second interdigital electrode pair, two adjacent bars of the
interdigital electrode 37 are connected to the samebus bar part 38. Natural vibration modes excited by AC currents supplied to the external terminals T21 and T22 are as shown inFIGS. 2A and 2B . Natural vibration modes excited by AC currents supplied across the external terminals T23 and T24 are as shown inFIGS. 2C and 2D . - The electrode structure shown in
FIG. 11A operates similar to the electrode structure shown inFIG. 1 . In the electrode structures shown inFIGS. 1 and 11A , the electrodes formed on the upper part of the piezoelectric substrate are connected to the external electrodes so that voltages having the same phase are applied thereto. On the other hand, the electrodes formed on the lower part of the piezoelectric substrate are connected to the external electrodes so that voltages having different phases are applied thereto. - A first variation of second embodiment will now be described with reference to
FIG. 11B . In an electrode structure shown inFIG. 11B , an interdigital electrode pair of 31 and 33 and an interdigital electrode pair of 35 and 37 are serially disposed. Natural vibration modes excited by an AC current supplied across external terminals T23 and T24 are as shown inFIGS. 2E and 2F . - According to the first variation of second embodiment utilizing the natural vibration modes shown in
FIGS. 2C and 2E , an antiresonace frequency can be adjusted by changing a driving signal level. - As shown in
FIGS. 1A , 9, and 10, the embodiments having the electrode structures having the electrodes formed on both the front and rear surfaces of the quartz substrate utilizes the bulk wave vibration modes such as a thickness shar vibration. A second variation of the second embodiment of the complex resonance circuit having interdigital electrodes, which also utilizes bulk waves of a thickness shear vibration mode, will now be described with reference toFIGS. 12A , 12B, and 12C. The bulk waves of the thickness shear vibrational modes are excited by applying voltages to the interdigital electrodes. - As shown in
FIG. 12A , two interdigital electrodes are formed on a front surface of an At-cut quartz substrate X4. Two interdigital electrodes are formed on a rear surface of the At-cut quartz substrate X4. Each of the interdigital electrodes is configured by a plurality of parallel bars. As shown inFIG. 12B , one interdigital electrode pair formed on the front surface is configured by the two interdigital electrodes which are substantially symmetric to each other in the horizontal direction. As shown inFIG. 12C , the other interdigital electrode pair formed on the rear surface is configured by the electrodes which are horizontally asymmetric in phase to each other with respect to center part thereof. - As shown in
FIG. 12B , the two interdigital electrodes on the front surface are substantially symmetric in the horizontal and vertical directions. The bars of the interdigital electrode are connected to the same electric potential. Thus, a vibration displacement of an excited vibration mode is substantially symmetric in the horizontal and vertical directions as shown inFIG. 2A . On the other hands, the bars of the interdigital electrode shown inFIG. 12C are connected to different electric potential at the center of the interdigital electrode. Thus, a vibration displacement of an excited vibration mode is substantially symmetric in the vertical direction and substantially asymmetric in the horizontal direction as shown inFIG. 2C . In the second variation of the second embodiment shown inFIG. 12 , unnecessary vibrations as shown inFIGS. 2B and 2D are not substantially excited. The excited natural vibration mode as shown inFIG. 2A appears to external terminals T31 and T33. The excited natural vibration mode as shown inFIG. 2C appears to external terminals T32 and T34. Therefore, the second variation of the second embodiment can suppress spurious vibration modes, and therefore, has a favorable frequency variable characteristic. - The second variation of the second embodiment shown
FIGS. 12A , 12B, and 12C may be modified as follows. Periodic interdigital electrodes and periodic groove portions, which are shorted or not shorted, may be disposed on the piezoelectric substrate so as to be adjacent to the interdigital electrodes ofFIGS. 12A , 12B, and 12C. The periodic interdigital electrodes and the periodic groove portions are adjacent to each other or uniformly spaced. The periodic interdigital electrodes and the periodic groove portions reflect excited vibrations, thus concentrating vibration energy of the excited vibration into the vicinity of the interdigital electrodes. A property improvement mean such as the periodic interdigital electrodes and periodic groove portions is utilized in a conventional surface wave device (including a filter and a resonator). - A third embodiment of the complex resonance circuit according to the present invention will now be described with reference to
FIGS. 13A to 13F . The third embodiment utilizes a bending vibration mode and has electrodes configured by a twin-tuning-fork structure, both ends of which are supported. -
FIG. 13A is a perspective view showing a X-cut quartz substrate having a twin-tuning-fork structure, both ends of which are supported. The quartz substrate shown inFIG. 13A has a structure similar to a conventional piezoelectric vibrator utilizing a twin-tuning-fork structure and a bending vibration mode. Firstly, components similar to the conventional piezoelectric vibrator are schematically described for the sake of simplicity. - As shown in
FIG. 13A , aquartz substrate 51 with a uniform thickness has a rectangular shape. A rectangular aperture is formed so as to pass completely through a center of thequartz substrate 51. Thequartz substrate 51 includes upper andlower parts bifurcation parts - Next, an arrangement and a connection of electrodes formed on the
quartz substrate 51 will now be described. As shown inFIG. 13B which is a cross-sectional view showing one part of thequartz substrate 51 taken along the A-A′ line ofFIG. 13A ,electrodes upper part 52. Theelectrodes FIG. 13C which is a projected diagram of the electrodes. In other wards, the fourelectrodes FIG. 13C is respectively formed on four surfaces of theupper part 52. InFIG. 13A , theelectrodes electrodes 61′ and 62′ are hidden behind theupper part 52. - A conventional tuning-fork type bending resonator is formed by forming four electrodes on four surfaces of the
lower part 53 of thequartz substrate 51. It is known that the conventional tuning-fork type bending resonator vibrates around at a resonance frequency in a vertical direction ofFIG. 13A in response to AC voltages applied to two external electrodes connected thereto. The vibration motion of the conventional tuning-fork type bending resonator in the vertical direction is similar to a vibration motion of a string in a vertical direction. A mode shape of the vibration displacement at theupper part 52 is shown inFIG. 13E . As shown inFIG. 13E , the vibration displacement has the highest point at a center portion of theupper part 52 and the smallest points at both ends of theupper part 52, in other wards, at the right and leftbifurcation parts - On the other hand, an absolute value of a vibration displacement of the
lower part 53 is similar to that of theupper part 52, but a direction of the vibration displacement of thelower part 53 is opposed to that of theupper part 52. Thus, a mode shape of the vibration displacement of thelower part 53 is an inversion of the curvature ofFIG. 13E . - In the third embodiment of the present invention, the
electrodes upper part 52 as shown inFIGS. 13B and 13C and connected as shown inFIG. 13C . In addition, electrodes separated at a center of thelower part 53 are formed as shown inFIG. 13D . The electrodes of thelower part 53 are different from the conventional tuning-fork type bending resonator. - As shown in
FIG. 13D , eightelectrodes 71 to 74 and 71′ to 74′ are formed on thelower part 53. The configuration of the eight electrodes will now be described from a view point of operations thereof. The third embodiment of the present invention includes the twin-tuning fork structure in which four electrodes shown inFIG. 13C are respectively formed on four surfaces of theupper part 52 and eight electrodes shown inFIG. 13D are formed on four surfaces of thelower part 53. The four electrodes of theupper part 52 are connected to theexternal electrodes FIG. 13C . The eight electrodes of thelower part 53 are connected to the external electrodes T43 and T44 as shown inFIG. 13D . - It is known that AC voltages applied to the
external terminals upper part 52 of thequartz substrate 51 ofFIG. 13A . The vibration motion of theupper part 52 is similar to a vertical vibration motion of a string. A vibration displacement of theupper part 52 in response to the AC applied voltages shows a mode shape as shown inFIG. 13E . Theupper part finger 52 has the largest vibration displacement at the center thereof and the smallest vibration displacement at both ends thereof, in other wards, around at the right and leftbifurcation parts upper part 52 is propagated into thelower part 53 via the right and leftbifurcation parts lower part 53 whose amplitude is similar to that of theupper part 52 and vibration direction is opposed to that of theupper part 52. - On the other hand, it is also known that an AC voltage applied across the
external terminals lower part 53 of thequartz substrate 51 ofFIG. 13A . The vibration motion of thelower part 53 is similar to a vertical vibration motion of a string. A vibration displacement of thelower part 53 in response to the AC applied voltages shows a mode shape as shown inFIG. 13F . Thelower part 53 has the largest vibration displacement at intermediate points between a center thereof and both ends thereof and the smallest vibration displacement at the center thereof and at both ends thereof, in other wards, around at the right and leftbifurcation parts upper part 52 is propagated into thelower part 53 via the right and leftbifurcation parts upper part 52 whose amplitude is similar to that of thelower part 53 and direction is opposed to that of thelower part 53. As shown inFIG. 13D , the electrodes of thelower part 53 are isolated into two electrode groups, one of which includes theelectrodes electrodes FIG. 13D . - In the case that the AC voltage is applied across the
external terminals lower part 53 is transferred into theupper part 52 via the right and leftbifurcation parts upper part 52 whose amplitude is similar to that of thelower part 53 and direction is opposed to that of thelower part 53. A mode shape of the vibration displacement of theupper part 52 is an inversion of the curvature ofFIG. 13F . - As described above, both of two natural vibration modes entirely appear in the twin-tuning-fork type resonator of the present invention. In a similar way of the first embodiment, an antiresonance frequency of the twin-tuning-fork type resonator can be controlled by adjusting amplitudes of signals respectively applied to the upper and lower parts.
- The first to third embodiments of the complex resonance circuit according to the present invention have been described. These embodiments utilize two natural vibration modes of a thickness shear vibration, a surface wave vibration, and a tuning fork longitudinal vibration.
- However, the complex resonance circuit according to the present invention is not limited to the first to third embodiments. The complex resonance circuit according to the present invention can be modified into another embodiment utilizing a piezoelectric vibrator which can excite a bending vibration, a longitudinal vibration, a face shear vibration, a width-extensional vibration, a thickness shear vibration, a thickness longitudinal vibration, a shear horizontal surface wave vibration, a SMR vibration, or a Stoneley surface wave. The complex resonance circuit according to the present invention includes two electrode pairs for independently driving at least two natural vibration modes of a piezoelectric vibrator. The at least two natural vibration modes are selected among a large number of natural vibration modes. Thus, the complex resonance circuit according to the present invention can eliminate a variable-reactance element and adjust a frequency by controlling a difference between two driving voltages respectively applied to the two electrode pairs.
- The complex resonance circuit according to the present invention utilizing a piezoelectric material is summarized as follows. Arrangements and shapes of electrodes formed on a piezoelectric substrate are configured so as to be substantially symmetric in the horizontal and vertical direction. A first pair of the electrodes connected to the same polarity and a second pair of the electrodes whose polarities are opposite to each other with respect to a center thereof are disposed. In other words, two electrode pairs for effectively concentration electric charges originated from two natural vibration modes are disposed. Each of the electrodes is configured so that the electric charges are applied.
- Therefore, the complex resonance circuit according to the present invention is configured so that a plurality of electrodes are formed on the same piezoelectric substrate and two exited natural vibration modes are independently controlled.
- First to sixth embodiments of the oscillation circuit according to the present invention will now be described. The first to sixth embodiments utilize the complex resonator according to the present invention.
- The first embodiment of the oscillation circuit according to the present invention, which is configured so as to adjust an oscillation frequency over a wide range around at an antiresonance frequency by controlling voltages applied to two external terminals, is firstly described.
- A conventional oscillation circuit oscillates around at a “resonance frequency”, whereas the oscillation circuit according to the present invention oscillates at an “antiresonance frequency” since the complex resonator according to the present invention essentially operates so as to adjust an antiresonance frequency.
- For the sake of oscillating a shunt circuit around at an antiresonance frequency, the oscillation circuit of the present invention is configured by T-shaped circuits connected to an amplifier. Each of the T-shaped circuits is configured by a series arm and a shunt arm. The series arm has two capacitors. The shunt arm is connected to the complex resonance circuit of the present invention. The oscillation circuit according to the present invention is completely different from a conventional oscillation circuit configured by n-shaped circuit connected to an amplifier. In the conventional oscillation circuit, a series arm is connected to a quartz oscillator and a shunt arm has two capacitors.
-
FIG. 14A is a block diagram showing a first embodiment of the oscillation circuit according to the present invention. The first embodiment includes the complex resonator according to the present invention. Apart 80 enclosed by a dotted line corresponds to the complex resonator (hereafter “piezoelectric vibrator”) according to the present invention which is schematically illustrated. External terminals T41, T42, T43, and T44 are similar to the external terminals of the embodiments of the complex resonance circuit according to the present invention which have already been described. The external terminals T42 and T44 of thepiezoelectric vibrator 80 are grounded. The external terminals T41 is connected to an attenuator ATT41 and two capacitors C1 and C2. The external terminals T43 is connected to an attenuator ATT41 and two capacitors C3 and C4. - An amplifier AMP41, which is configured by at least one conventional transistor or at least one complex circuit having at least one conventional transistor, includes an input terminal T58, an output terminal T59 whose output phase is opposed to an input phase of the input terminal T58, and an output terminal T65 whose output phase is same as the input phase of the input terminal T58.
- The antiphase output terminal T59 of the amplifier AMP41 is divaricated into terminals T51 and T54 which are connected to four capacitors C1 to C4 and the
piezoelectric vibrator 80 via the attenuators ATT41 and ATT42, respectively. The terminals T51 and T54 are also connected to an intermediate tap T57. The oscillation circuit shown inFIG. 14A is configured by a negative feedback loop circuit of the amplifier AMP41. - The negative feedback circuit loop corresponds to a negative feedback path connecting from the output terminal of the amplifier to the input terminal. A path connecting from the output terminal T59 to the intermediate tap T57 configures a power distribution circuit. The power distribution circuit includes two power distribution paths, one of which is configured by a path connecting from the intermediated tap T51 to the intermediate tap T57 and the other of which is configured by a path connecting from the intermediated tap T54 to the intermediate tap T57. In addition, in the two electric power supply paths, a first electric current branch path is configured by two paths: a path over the intermediate taps T52→T53→T57 and a path over the intermediate taps T55→T56→T57. A second electric current branch path is configured by two paths: a path connecting from a middle point between the intermediated taps T52, T53 to the earth potential via the
piezoelectric vibrator 80 and a path connecting from a middle point between the intermediated taps T55, T56 to the earth potential via thepiezoelectric vibrator 80. - One end of a series circuit having a capacitor C11 and a coil L12 is connected to the input terminal T58 of the amplifier AMP41 and the other end of the series circuit is grounded. One end of a series circuit having capacitors C9 and C10 is connected to the input terminal T58 and the other end of the series circuit is grounded. A circuit loop connecting from a middle point between capacitors C9, C10 to the output terminal T65 via a resistance R8 is configured. This circuit loop corresponds to a positive feedback circuit loop of the amplifier AMP41.
- The negative feedback circuit loop configures a negative feedback path connecting from the output terminal of the amplifier to the input terminal.
- Even if a value of the resistance R8 is 0, that is, the resistance R8 is shorted, the amplifier AMP41 substantially operates, which is similar to a conventional oscillation circuit.
- A function of the positive-feedback circuit loop will now be described. A circuit including the input terminal T58 of amplifier AMP41, the output terminal T65, the coil L12, the capacitors C11, C9, C10, and the resistance R8, configures a conventional Colpitts oscillator (Clapp oscillator). Element values of the circuit are arbitrarily configured, and if a gain of the amplifier AMP41 has a sufficient value, the oscillation circuit will start and maintain its oscillation.
- And, an oscillation frequency in this case is approximately a resonance frequency of a synthesis capacity of a series connection having the coil L12 and three capacitors C11, C9, and C10. In the first embodiment, an oscillation frequency around at an antiresonance frequency generated by the complex resonance circuit including the
piezoelectric vibrator 80 is selected. - The capacitor C11 has a DC voltage cutoff function so that a DC bias voltage having a proper amplitude is applied to the amplifier AMP41.
- The amplifier AMP41 and a band-pass filter FIL41 are configured so as to have amplification gains sufficient for compensating a loss in the oscillation of the entire oscillation circuit, and thus the
piezoelectric vibrator 80 excites an antiresonance frequency. The amplifier AMP41 and the band-pass filter FIL41 have such a phase characteristic that thepiezoelectric vibrator 80 oscillates around at an antiresonance frequency. The amplifier AMP41 and the band-pass filter FIL41 may have a function, for instance, an AGC mechanism, so as to hold an output level at an output end (the intermediate tap 59) of the amplifier AMP41 constant. - A principle of the oscillation circuit according to the present invention will now be described. The oscillation circuit oscillates around at an antiresonance frequency of the complex resonance circuit according to the present invention. Since an upper half part having the intermediate taps 52,53 and the external terminals T41, T42 of the
piezoelectric vibrator 80 is configured similar to a lower half part having the intermediate taps 55,56 and the external terminals T43, T44 of thepiezoelectric vibrator 80, only the upper half part is described. - The upper part having the intermediate taps 52, 53 and the external terminals T41, T42 of the
piezoelectric vibrator 80 configures a T-shaped circuit. That is, the T-shaped circuit is configured by two parts: one of which is a shunt arm connected to the external terminals T41 and T42 of thepiezoelectric vibrator 80 and the other of which is a series arm connected to the two capacitors C1 and C2. The negative feedback circuit is configured by two T-shaped circuits, thus allowing for an effect similar to an impedance inverting function as shown inFIG. 15 . The effect is accompanied by the amplification gain the amplifier AMP41. - The negative feedback circuit is configured by two T-shaped circuits, thus a frequency characteristic curve b5 shown in
FIG. 15 which is vertically reversed to the frequency characteristic curve b3 ofFIG. 5 is observed. The vertical axis ofFIG. 15 corresponds to an applied voltage at the intermediate tap 65 which is divided by an applied voltage at the intermediate tap 58. The horizontal axis ofFIG. 15 corresponds to a frequency. - The frequency characteristic curve b5 of
FIG. 15 , which is vertically reversed to the frequency characteristic curve b3 ofFIG. 5 , is observed. Thus, it is apparently understood that an antiresonance frequency of the piezoelectric vibrator of the present invention is viewed as a resonance frequency of a conventional piezoelectric vibrator. Therefore, the oscillation circuit can be configured by the positive and negative feedback circuits including the T-shaped circuits and the amplifier having a predetermined frequency characteristic. - Next, a method of continuously adjusting a frequency by changing voltages applied to two external terminals of the piezoelectric vibrator will now be described. As described above, when the voltages respectively applied to the external terminals T41 and T43 of the piezoelectric vibrator according to the present invention are changed, an antiresonance frequency fp is adjusted as shown in
FIG. 6 . In the oscillation circuit shown inFIG. 14A , an adjustment of the antiresonance frequency fp is performed by adjusting a difference in attenuation values between two attenuators: one of which is ATT41 between theintermediate taps - A power output of the amplifier at the
intermediate tap 51 is attenuated by the attenuator ATT41 so that a sufficient voltage is applied thereto. And then, the voltage is applied to the external terminal T41 of the piezoelectric vibrator via the capacitor C1. By arbitrarily adjusting an attenuation value of the attenuator ATT41, the applied voltage on the external terminal T41 can be arbitrarily controlled. In the same way, an applied voltage on the external terminal T43 can be arbitrarily controlled by arbitrarily adjusting an attenuation value of the attenuator ATT42. - By controlling each attenuation value of the two attenuators ATT41 and ATT42, the applied voltages on the external terminals T41 and T43 can be arbitrarily adjusted. Therefore, a value of an antiresonance frequency fp can be arbitrarily adjusted as shown in
FIG. 6 . - Even if the four capacitors C1 to C4 are replaced by four coils, four resistances, or combinations of capacitors, coils, and resistances, a similar effect will be obtained. An output impedance of a commercial attenuator is 50Ω. Output impedances of the attenuators ATT41 and ATT42 of the first embodiment are not limited to this value. When the output impedances of the attenuators ATT41 and ATT42 are extremely small, for example, no less than 1Ω, the attenuators ATT41 and ATT42 show preferable characteristics. In addition, if the attenuators ATT41 and ATT42 are replaced by resistance attenuators, each of which has an internal element including a resistance, a similar effect will be obtained. And even if the attenuators ATT41 and ATT42 are replaced by attenuators, each of which has a reactance element including a capacitor and a coil, a similar effect will be obtained.
- The first embodiment of the oscillation circuit according to the present invention operates around at an antiresonance frequency fp of the
piezoelectric vibrator 80. Since the piezoelectric vibrator shows a high impedance characteristic around at the antiresonance frequency, it is required to pay attention to a variation of a stray capacity generated around the piezoelectric vibrator at the time when the oscillation circuit is packaged. For the sake of reducing an influence of the stray capacity and producing an easy-to-use oscillation circuit, it is preferable that circuit elements including, for example, the intermediate taps 52, 53, 55, and 56, the four capacitors C1 to C4, and thepiezoelectric vibrator 80 ofFIG. 14A are packaged in the same cage. And thus, the influence of the variation of the stray capacity will be reduced by an overcoated part in the cage. As described above, four capacitors C1 to C4 may be replaced by four coils, four resistances, or the combinations of coils, capacitors, and resistances. - A variation of the second embodiment of the oscillation circuit will now be described with reference to
FIG. 14B . The oscillation circuit shown inFIG. 14A is modified into an oscillation circuit shown inFIG. 14B as follows. - First of all, the attenuator ATT41 of
FIG. 14A is removed, and then the intermediate tap T51 and T52 are shorted to each other. Similarly, the attenuator ATT42 is removed, and then the intermediate tap T54 and T55 are shorted to each other. The removed attenuator ATT41 is connected between theexternal terminal 42 and the earth potential of thepiezoelectric vibrator 80. Similarly, the removed attenuator ATT2 is connected between theexternal terminal 44 and the earth potential of thepiezoelectric vibrator 80. In such a circuit structure as shown inFIG. 14B , attenuation values of the attenuators ATT1 and ATT2 are controlled, so that electric potential differences between theexternal terminals piezoelectric vibrator 80 and between theexternal terminals piezoelectric vibrator 80 can be adjusted. - Next, a second embodiment of the oscillation circuit according to the present invention for cancelling parallel capacities of a piezoelectric vibrator will now be described with reference to
FIG. 16 .FIG. 16 is a schematic circuit diagram showing the second embodiment of the oscillation circuit according to the present invention. As shown inFIG. 16 , the second embodiment is configured so thatcircuits 90 and 91 enclosed by dotted lines are added to the circuit ofFIG. 14A . Since both of the additional circuits have the same components and functions, only thecircuit 90 will be described. - The
circuit 90 includes capacitors C1′, C2′, and CO1′ and a differential amplifier AMP90. It is configured that the two capacitors C1′ and C2′ have the same capacitance value as that of capacitors C1 and C2. It is also configured that a capacitance value of the capacitor CO1′ is same as that of a parallel capacity CO1 connected between the external terminals T41 and T42 of thepiezoelectric vibrator 80. Power outputs of the capacitor C2 and the capacitor C2′ are connected to positive and negative input terminals of the differential amplifier AMP90 via an intermediate tap T53 and T53′, respectively. - In the second embodiment, the parallel capacity CO1 between the external terminals T41 and T42 of the
piezoelectric vibrator 80 can be cancelled by a bridge balance phenomenon. In the same way, a parallel capacity CO2 between the external terminals T43 and T44 can be canceled by the circuit 91 enclosed by the dotted line ofFIG. 16 . - A third embodiment of the oscillation circuit according to the present invention for cancelling parallel capacities of a piezoelectric vibrator in a different way will now be described with reference to
FIG. 22A . - As shown
FIG. 22A , the third embodiment of the oscillation circuit according to the present invention includes a T-shaped circuit across an AC power source e1 and a load resistance RL. A conventional piezoelectric vibrator Q1 is connected to a middle point of a series arm having a capacitor C1 and a coil L2. - The piezoelectric vibrator Q1 in the circuit of
FIG. 22A is formed from a HC-49/U type AT-cut quartz resonator whose resonance frequency is 9.9952 MHz. A design of and a specification of the piezoelectric vibrator is the same as those described above. A nominal capacitance value of the capacitor C1 is 2.5 pF and a nominal inductance value of the coil L2 is 27 μH. - Configuration conditions of circuit element constants of the T-shaped circuit of
FIG. 22A will now be described with reference toFIG. 22B . - When a capacitance value of the parallel capacity of the piezoelectric vibrator Q1 is given by CO1, it is configured that a sum (CO1+C1) of the capacitance value of the parallel capacity CO1 and the capacitance value of the capacitor C1 is in the range of an operation frequency bandwidth (an oscillation frequency bandwidth). It is also configured that a resonance frequency determined from an inductance value of the coil L2 is in the range of the operation frequency bandwidth (the oscillation frequency bandwidth). When the capacitance values of the CO1 and the C1 are relatively small, it is possible to experimentally reconfigure the capacitance values and the resonance frequency in consideration of an influence of the stray capacity.
-
FIG. 23 is a graph showing an experimental frequency characteristic curve for the third embodiment shown inFIG. 22A . The horizontal axis ofFIG. 23 corresponds to a frequency, and the vertical axis corresponds to an absolute value of an attenuation value. It is understood fromFIG. 23 that the experimental frequency characteristic curve is symmetric with respect to the frequency and that the influence of the parallel capacity is reduced and substantially cancelled. Since the attenuation value shown inFIG. 23 has a maximum point at a frequency 9.9952 MHz which corresponds to a resonance frequency of the piezoelectric vibrator Q1, it is understood that an impedance inversion effect is also generated. - It is to be noted that a position of the coil is modified in the series arm. The position of the coil of
FIG. 22A is modified as shown inFIG. 22C . As shown inFIG. 22C , even if a coil L1 is positioned at a position where the capacitor C1 ofFIG. 22B is disposed and a capacitor C2 is positioned at a position where the coil L2 ofFIG. 22B is disposed, a similar effect will be obtained. - One of the circuit element constants of the T-shaped circuit, which has not been described, will now be described. According to the present invention, the one of circuit element constants of the T-shaped circuit is utilized for optimizing an effective Q-value (an effective sharpness of the peak resonance) of the piezoelectric vibrator Q1 (the complex resonator according to the present invention) so that the effective Q-value is not degraded around at an antiresonance frequency. Configuration conditions of the optimized circuit constants are as follows.
- In
FIG. 22B , it is firstly configured that a capacitance value of the capacitor C1 connected to a series arm is ten times or less than a capacitance value of the parallel capacity CO1. It is configured that the parallel capacity CO1 ofFIG. 22B is the parallel capacity CO1 of the piezoelectric vibrator Q1 ofFIG. 22A . Under such the configuration condition of the circuit element constants, a resonance impedance value of a resonance part including the capacitor C1 and the coil L2 of the T-shaped circuit becomes a sufficient large value, so that the piezoelectric vibrator Q1 connected to a shunt arm remarkably exhibits an impedance shunt effect. - In the circuit of
FIG. 22B , it is experimentally confirmed that the parallel capacity cancelling effect and the impedance inversion effect are obtained under the following condition. It is configured that a resonance frequency which is determined from the sum (CO1+C1) of the capacitance values of the parallel capacity CO1 of the quartz resonator Q1 and the capacitance value of the capacitor C1 is within the range of a working frequency bandwidth. In addition, it is configured that the inductance value of the coil L2 is in the range of the working frequency bandwidth. This behavior is theoretically analyzed with reference to a circuit shown inFIG. 24A which is an equivalent circuit ofFIG. 22B . - In
FIG. 24A , a T-shaped circuit is connected across an AC power source e1, a resistance R1, and a load resistance RL. The T-shaped circuit includes a series circuit configured by impedances Z1 and Z2. The T-shaped circuit also includes a parallel circuit configured by impedances Zp and Zs, which parallel circuit is connected to a middle point of the series circuit. The impedance Zp corresponds to a parallel capacity part of the piezoelectric vibrator. The impedance Zs corresponds to an impedance of the series connection of L11, C11, and r11 of the piezoelectric vibrator. - For the purpose of analyzing a performance of the circuit shown in
FIG. 24 A, it is preferable that a cascade matrix element of the T-shaped circuit between intermediate taps T52 and T53 is firstly calculated, and then an admittance matrix element Y21, which is convenient to estimate the parallel capacity cancelling effect, is calculated. The following equation is obtained by performing such the calculating processes. -
-
- if a condition given by an
equation 5 is fulfilled, theequation 4 can be simply rewritten by the following equation. -
- It is necessary to pay attention to the right side of the
equation 6 in which the numerator has only the impedance Zs of the series connection configured by L11, C11, and r11. - The numerator of the
equation 6 has only the impedance Zs. Zp is eliminated in theequation 6, which means that the impedance Zp of the parallel capacity CO1 is cancelled, and in addition, means that the admittance Y21 is proportional to the impedance Zs and the inverted impedance Zs is converted to the admittance. - Next, the
equation 5 giving the condition will now be described, under which the parallel capacities are cancelled and the impedance is inverted. Since theequation 5 holds even if Z1 and Z2 are replaced with each other, the following equation is obtained by rearrangingequation 5 with respect to Z2. -
- As described above, since the impedance Zp corresponds to the parallel capacity CO1 of the piezoelectric vibrator, the impedance Zp is given by the following equation.
-
- In addition, since the impedance Z1 is an impedance of a capacitor having the capacitance value C1, the impedance Z1 is given by the following equation.
-
- The following equation is obtained by substituting the equation 9 and the
equation 8 forequation 7. -
- Since the impedance Z2 of the
equation 10 is an impedance of a coil having the inductance value L2, the impedance Z2 is given by the following equation. -
- The following equation is obtained by substituting
equation 11 forequation 10. -
- When the resonance angular frequency ω of the
equation 12 is given by the following equation, the condition given by theequation 10, that is, theequation 5 will be completely fulfilled. -
- Here, the resonance angular frequency ωc of equation 13 is referred to as a parallel capacity cancelling resonance angular frequency. Although the
conditional equation 5 is completely fulfilled if the parallel capacity cancelling resonance angular frequency ωc has one value, a condition that the left side of theconditional equation 5 is approximately 0 is fulfilled even if the parallel capacity cancelling resonance angular frequency approximately ωc has the approximate value. Theequation 4 is approximated by theequation 6 since the second term of the denominator of theequation 4 has a value less than 1. The correctness of the above-mentioned theoretical analysis is proven by the measurement result shown inFIG. 23 . - The third embodiment of the oscillation circuit according to the present invention has been described. In the third embodiment, the impedance Z2 of
equation 10 corresponds to the coil. The next embodiment where the impedance Z2 corresponds to a “negative capacity” will be described. An oscillation circuit having a negative capacity is disclosed in, for example, “Japanese Patent No. 3400165”. In this case, a frequency dependence of the negative capacity is similar to a frequency dependence of the left side of theequation 5. Thus, a condition given by theequation 10 is fulfilled over a wide rage of frequency. - A fourth embodiment of the oscillation circuit according to the present invention will now be described with reference to
FIG. 25 . An oscillation circuit shown inFIG. 25 has two T-shapes circuits ofFIG. 22A , each of which has the complex piezoelectric vibrator according to the present invention connected to a shunt arm, the capacitor, and the coil. - As shown in
FIG. 25 , in acomplex vibrator 80, two conventional piezoelectric vibrators Q1 and Q2 are connected across theexternal terminals external terminals - Each nominal capacitance value of the capacitors C1 and C2 is 2.5 pF and each nominal inductance value of the coils L2 and L4 is 27 μH.
- Conditions of circuit element constants of the T-shaped circuits of
FIG. 25 betweenintermediate taps 52 and 53 (including the quartz resonator Q1) and betweenintermediate taps 55 and 56 (including the quartz resonator Q2) are configured by adopting the conditions described with reference toFIG. 22B thereto. - A circuit between
intermediate taps 59 and 57 shown inFIG. 25 is connected across a frequency variable type high frequency signal generator SG and a level measuring instrument L1 as shown in circuit ofFIG. 3 . And then, a relation between an antiresonance frequency and a difference in attenuation values between two attenuators ATT1 and ATT2 is shown inFIG. 26 . - It is understood from
FIG. 26 that depending on the difference of attenuation values between two attenuators, a value of an antiresonance frequency can be continuously adjusted over a wide rage up to 98.6% of a frequency difference between resonance frequencies of the two piezoelectric vibrators. An absolute value of the maximum normalized frequency varies over a wide rage up to 978 ppm. - A circuit configuration including the two circuits, each of which can cancel the parallel capacity, is characterized by a resonance sharpness (an effective Q value) which is substantially constant between the resonance frequencies of the quartz resonators Q1 and Q2.
- In
FIG. 25 , it is experimentally clarified that the antiresonance frequency is correlated with the difference in the attenuation values between the two attenuators ATT1 and ATT2. The correlation will now be theoretically described. - In
FIG. 25 , the shunt arms includeexternal terminals piezoelectric vibrator 80. Elements A1, B1, C1, and D1 of a cascade matrix F1 is calculated by using circuit element values across the intermediate taps T52 and T53. - In the same way, in the circuit of
FIG. 25 , the shunt arms includeexternal terminals piezoelectric vibrator 80. Elements A2, B2, C2, and D2 of a cascade matrix F2 is calculated by using circuit element values across the intermediate taps T55 and T56. - An analytical result is shown in an equivalent circuit of
FIG. 27A . As shown inFIG. 27A , a voltage V1 corresponds to a voltage across an intermediate tap T52 and a ground. A voltage V2 corresponds to a voltage between an intermediate tap T55 and the ground. A voltage V3 corresponds to a voltage between an intermediate tap T57 and the ground. The voltages V1 and V2 can be adjusted by varying only the attenuation values of the attenuators ATT1 and ATT2. - The equivalent circuit shown in
FIG. 27A can be replaced by an equivalent circuit shown inFIG. 27B . Here, Zss1 denoted inFIG. 27B is an impedance in a direction from an intermediate tap T52 ofFIG. 27A to a power supply. Zss2 is an impedance in a direction from an intermediate tap T55 ofFIG. 27A to the power supply. In addition, an AC power source e1 ofFIG. 27B is configured so that a voltage at the intermediate tap T52 ofFIG. 27B is equal to the voltage V1 ofFIG. 27A . An AC power source e2 ofFIG. 27B is configured so that a voltage at the intermediate tap T55 ofFIG. 27B is equal to the voltage V2 ofFIG. 27A . - Cascade matrixes F1 and F2 of
FIG. 27B can be replaced by Z01 and Z02, respectively as shown inFIG. 27C . The replacement is performed on the basis of Thevenin's theorem by using elements of the cascade matrixes. Here, the impedances Z01 and Z02 ofFIG. 27C are given by the following equation, respectively. -
- In addition, power-supply voltages e01 and e02 of
FIG. 27C are given by the following equation, respectively. -
- Here, for the sake of deriving the relation between an antiresonance frequency of the circuit of
FIG. 27B and voltages V1 and V2, it may be configured that Zss1, Zss2, and RL are equal to zero. Thus, an output current intensity IL is given by the following equation under a condition that C1=C3 and L2=L4. -
- Here, V1 corresponds to a voltage across the intermediate tap T52 and the ground. V2 corresponds to a voltage across the intermediate tap T55 and the ground. ZS1 is an impedance of the series arm connected to the piezoelectric vibrator Q1. ZS2 is an impedance of the series arm connected to the piezoelectric vibrator Q2.
- The
equation 18 is formally similar to theequation 1. The voltage V1 and V2 are multiplied by the impedances ZS1 and ZS2 of the two series arms, respectively. C1 divided by L2 is constant whose value does not show a frequency response characteristic, which means that a preferable Q-value is obtained over the wide range of a variable frequency. - Therefore, the correlation between the voltages V1 and V2 and the antiresonance frequency in the fourth embodiment is given by the
equation 3. It is understood from the experimental results ofFIGS. 20 and 26 that the correlation between the voltages V1 and V2 and the antiresonance frequency is followed by theequation 3. - Therefore, the parallel capacities across the external terminals T41, T42 and between the external terminals T43, T44 can be reduced, and thus only the series arms causing the resonance frequencies are remarkably effective. That is, influences of the unnecessary parallel capacities can be reduced by using the complex resonance circuit according to the present invention. The complex resonance circuit according to the present invention (piezoelectric vibrator) utilizes a property of the piezoelectric vibrator vibrating around at a antiresonance frequency fp at which an impedance is comparatively high, so that an improvement effect of figure of merit (corresponding to a Q-value of the piezoelectric vibrator divided by the capacitance ratio) appears remarkably, and thus a generation of an oscillation power output with a high quality can be expected.
- The first to forth embodiments of the oscillation circuit according to the present invention utilizing two natural vibration modes has been described. The first to forth embodiments can be modified as follows. By applying, for example, three or more voltages, three or more natural vibration modes are utilized. In this case, a similar effect will be achieved.
- A fifth embodiment of the oscillation circuit which directly oscillates an antiresonance frequency will now be described with reference to
FIG. 28 . - A basic idea of the fifth embodiment is as follows. An oscillation circuit of the fifth embodiment includes two T-shaped circuits of
FIG. 25 connected to the complex resonance circuit 80 (also referred to as “piezoelectric vibrator”) of the present invention. The oscillation circuit is configured so as to maintain a loop gain thereof at which thecomplex resonance circuit 80 can vibrates at a sharp antiresonance frequency. -
FIG. 28 is a block diagram showing the fifth embodiment of the oscillation circuit according to the present invention. The oscillation circuit ofFIG. 28 has the complex resonance circuit according to the present invention corresponding to a part enclosed by a dotted line. An amplifier AMP41 has a positive input terminal 45 (connected to an intermediate tap 60), a negative input terminal 46 (connected to an intermediate tap 61), and a positive output terminal 47 (connected to an intermediate taps 63, 64). - The fifth embodiment of the oscillation circuit according to the present invention for oscillating an antiresonance frequency is required to fulfill the following three basic conditions.
- A first condition is correlated with a positive feedback loop. As shown in
FIG. 28 , a series connection circuit of a coil L5, a capacitor C6, and a resistance R3 is connected to the positive output terminal 47 of the amplifier AMP41 via the intermediate tap 63. The series connection circuit is also connected to the positive input terminal 45 of the amplifier AMP41 via theintermediate tap 60. A resistance R4 is connected to a middle point between the resistance R3 and anintermediate tap 60, and in addition, connected to an earth potential. A positive feedback loop is configured by a loop circuit connected from the positive output terminal 47 to the positive input terminal 45 of the amplifier AMP41. If a loop gain of the positive feedback loop is more that 1, the oscillation circuit oscillates at a predetermined frequency whose range is variable. An inductance value of the coil L5 and a capacitance value of the capacitor C6 are configured so that a series resonance frequency determined therefrom is equal to the predetermined frequency. On the other hand, the resistances R3 and R4 are used for adjusting the loop gain of the positive feedback loop. - A second condition is correlated with a negative feedback loop. As shown in
FIG. 28 , two T-shaped circuits are configured. One of the T-shaped circuits includes a coil L2 and a capacitor C1 connected betweenintermediate taps external terminals piezoelectric vibrator 80. The other of the T-shaped circuits includes a coil L4 and a capacitor C3 connected betweenintermediate taps external terminals piezoelectric vibrator 80. - Each of the two T-shaped circuits configuring a negative feedback loop shows a frequency characteristic curve as shown in
FIG. 23 . If the amount of a negative feedback of the T-shaped circuits is decreased only at an antiresonance frequency fp, the loop gain of the positive feedback loop will be more than 1. Thus, the oscillation circuit ofFIG. 28 can oscillates at the antiresonance frequency fp. - A third condition is correlated with a stabilization of a DC bias voltage. As shown in
FIG. 28 , a series circuit is configured by a resistance R5 and a parallel circuit having a coil L7 and a capacitor C8. One end of the series circuit is connected to the positive output terminal 47 of the amplifier AMP41 via the intermediate tap T64. The other end of the series circuit is connected to the negative input terminal 46 of the amplifier AMP41 via an intermediate tap T61. One end of a resistance R6 is connected to a middle point between the resistance R5 and the intermediate tap T61. The other end of the resistance R6 is connected to an earth potential. An inductance value of the coil L7 and a capacitance value of the capacitor C8 are configured so that a parallel resonance frequency determined therefrom is equal to the predetermined frequency. - The negative input terminal 46 of the amplifier AMP41 is connected to the
intermediate tap 61, thus a negative feedback loop is configured by a loop connecting from the positive output terminal T47 to the negative input terminal T46 via the intermediate tap T64, the series circuit having the resistance R5 and the parallel circuit having the coil L7 and the capacitor C8, and the intermediate tap T61. Since a DC current also conducts through the negative feedback loop via the coil L7 configuring the loop, the negative feedback loop has a function of stabilizing the DC bias voltage from the oscillation circuit starts to oscillate until an oscillation frequency is saturated. By changing values of the resistances R5 and R6, the DC bias voltage and a loop gain of the negative feedback loop can be mainly adjusted. - When the three conditions are fulfilled, the oscillation circuit of
FIG. 28 can output a stable oscillation power of an antiresonance frequency. - A variation of the fifth embodiment of
FIG. 28 will now be described. - In the variation of the fifth embodiment of
FIG. 28 , reactance elements across the intermediate taps 62 and 63 ofFIG. 28 is replaced by at least one resistance element or at least one resistance element together with at least one reactance element. - In addition, the amplifier AMP41 may be replaced by an amplifier having only one positive input terminal and two output terminals. The positive input terminal corresponds to the positive input terminal T45 of
FIG. 28 . The two output terminals correspond to the positive output terminal T47 ofFIG. 28 and a negative output terminal T48 (not shown). In this case, the negative input terminal T46 is disconnected from the intermediate tap T61, and then the intermediate tap T61 is connected to the intermediate tap T60. In addition, the intermediate tap T63 is disconnected from the intermediate tap T64, and then the positive output terminal T47 is connected to the intermediate tap T63. The negative output terminal T48 is connected to the intermediate tap T64. The variation of the fifth embodiment can similarly oscillate at an antiresonance frequency fp. - In the first and fifth embodiments of the oscillation circuit described above, for the purpose of controlling the voltages applied across the terminals T41 and T42 and the external terminals T43 and T44 of the piezoelectric vibrator, the attenuation values of the attenuators are adjusted while holding the power output of the amplifier constant. Even if the attenuators are replaced by output voltage controlling type amplifiers, a similar effect will be achieved. If the output voltage controlling type amplifier has a small output impedance value in comparison with the value of the two equivalent resistances of the piezoelectric vibrator (for instance, r1 and r2 of
FIG. 8A ), degradation of a Q-value (sharpness of the peak resonance) of an antiresonance frequency will be reduced at the time when the oscillation circuit is implemented. - Furthermore, if the differential amplifiers AMP90 and AMP91 shown in
FIG. 16 has a small input impedance value in comparison with the two equivalent resistances of the piezoelectric vibrator (for instance, r1 and r2 ofFIG. 8A ), degradation of a Q-value of an antiresonance frequency will be reduced at the time when the oscillation circuit is implemented. - The operation amplifiers AMP90 and AMP91 of
FIG. 16 utilize a bridge balance phenomenon. Even if each of the attenuators ATT41 and the ATT42 is replaced by a push-pull output type amplifier, a modified circuit has effects similar to the circuit. - As described above, the first to fifth embodiments of the oscillation circuit according to the present invention eliminating variable reactance elements such as a variable-capacitance diode can adjust a frequency. A performance of the piezoelectric vibrator of the present invention can be more improved by providing a conventional variable reactance element together.
- A sixth embodiment of the oscillation circuit according to the present invention will now be described. The sixth embodiment includes the piezoelectric vibrator according to present invention and further includes conventional variable reactance elements. For instance, a capacitance value of a variable-capacity diode varies depending on a voltage applied thereto. A variable reactance element such the capacity variable diode has two terminals, and thus, operates similar to a capacitor (capacity) and a coil (inductance) having two terminals. Here, one terminal of an element having two terminals is referred as to P and the other terminal to Q.
- It will now be described in reference to the circuit of
FIG. 14A that an oscillation frequency of the oscillation circuit can be adjusted by changing a position of the variable reactance element. For the sake of adjusting an oscillation frequency of the oscillation circuit, one terminal P of the variable reactance element may be only connected to, for instance, either one of theexternal terminals piezoelectric vibrator 80 ofFIG. 14A . The other terminal Q of the variable reactance element is connected to any positions in the oscillation circuit ofFIG. 14A excluding the terminal P of the variable reactance element. Thus, an antiresonance frequency can be adjusted. InFIG. 14A , theexternal terminals piezoelectric vibrator 80 are referred as to “hot points”. If the variable reactance element is positioned at a position between thepoint 41 and the earth potential (the earth) or between thepoint 42 and the earth potential, an antiresonace frequency can be adjusted with a high sensitivity. - The sixth embodiment has two means, one of which is a variable-frequency mean for utilizing the present invention and the other of which is a variable-frequency mean for utilizing the variable reactance element. For example, a radio communications system utilizes the two means for the purpose of switching a channel and for modulating a signal. The complex resonance circuit of the present invention has two series arms whose equivalent circuit constants are dependent on voltages applied thereto. By utilizing this behavior, a variable-frequency filter capable of controlling a frequency characteristic can be configured.
- The measuring circuit shown in
FIG. 3 andFIG. 25 utilizing one of the above-described complex resonators (hereafter MR) having the piezoelectric vibrator etc. according to present invention really realizes a basic band section of a band rejection filter (hereafter BRE). The oscillation circuits shown inFIGS. 14 and 28 configured by the negative feedback circuit having one MR and four capacitors include a circuit part realizing a basic band section of a band pass filter (hereafter BTE). The band path filter is shown inFIGS. 17A and 17B . These four capacitors shown inFIGS. 14 and 28 may be replaced by four coils, four resistances, or combinations of them. - Next, an embodiment of the filter according to the present invention will now be described as a band pass filter with reference to
FIG. 17B . A circuit structure ofFIG. 17 B is configured by connecting in parallel an inverting amplifier between the intermediate taps T59 and T57 ofFIG. 25 . Thus, a negative feedback loop is configured in the circuit ofFIG. 17B . - The oscillation circuit of
FIG. 25 shows an antiresonant characteristic as shown inFIG. 23 from theequation 18. The circuit ofFIG. 25 configures a negative feedback part of the inverting amplifier, so that a negative feedback is applied on the circuit ofFIG. 17 B on the basis of an antiresonant characteristic thereof. A relation between voltages at intermediate taps T59 and T57 is reversed in its magnitude in similar with the case ofFIG. 15 , and thus the circuit ofFIG. 17 shows a band-pass characteristic. - As an example of the circuit of
FIG. 17B , a filter, in which a frequency characteristic thereof can be controlled by changing voltages V1 and V2 applied thereto, will now be described. InFIG. 17A , if the voltage V1 at the intermediate tap T52 of a negative feedback part and the voltage V2 at the intermediate tap T55 are changed, an antiresonance frequency of the negative feedback part depends on a ratio of both voltages as shown inFIG. 26 . A pass-band characteristic of the circuit ofFIG. 17B can be controlled by the applied voltages V1 and V2. - When an operational amplifier and a NAND circuit (an inverting gate circuit) are used as the inverting amplifier, it is required that a mean for stabilization of a DC bias voltage connected to the earth potential at the intermediate taps T61 and T64 etc. is provided with, for example, the oscillation circuit having the amplifier shown in
FIG. 28 . - For the sake of configuring a higher-order filter, a method of cascade connections having a plurality of basic sections used in a conventional filter is used. By connecting in parallel the basic sections (MRE and MTE), an attenuation gradient can be largely increased. In
FIG. 17B , attenuation values of two attenuators ATT1 and ATT2 are controlled for changing the frequency of the filter. The attenuators may be replaced by a conventional attenuators capable of electrically changing an attenuation value. - A variable-frequency band-pass filter utilizing the oscillation circuit according to the present invention has been described. Since the sharpness of the peak resonance of the piezoelectric vibrator is favorable, it is expected that an ideal filter will be realized by changing a narrowband band-pass filter.
Claims (6)
1. A piezoelectric vibration device comprising:
a single piezoelectric substrate;
at least three electrode pairs formed on said single piezoelectric substrate; and
two external connection terminal pairs,
wherein
said three electrode pairs are connected to said two external connection terminal pairs so that two different vibration modes individually appear at said two external connection terminal pairs.
2. A piezoelectric vibration device comprising:
a single piezoelectric substrate;
at least four electrode pairs formed on said single piezoelectric substrate; and
two external connection terminal pairs,
wherein
said four electrode pairs are connected to said two external connection terminal pairs so that only two different vibration modes individually appear at said two external connection terminal pairs and a vibration mode excluding said two different vibration modes dose not appear at said two external connection terminal pairs.
3. A piezoelectric vibration device according to claim 1 ,
wherein
said electrode pairs are rear and front surface electrode pairs, both rear and front surface electrodes are opposite to each other so as to sandwich said substrate.
4. A piezoelectric vibration device according to claim 3 , further comprising two negative and positive external electrode pairs,
wherein
one of said rear and front surface electrode pairs is connected to one of said two negative and positive external electrode pairs, and
two of said rear and front surface electrode pairs respectively having opposite polarities are connected to the other of said two negative and positive external electrode pairs.
5. A piezoelectric vibration device according to claim 1 ,
wherein
each of said electrode pairs is formed substantially in parallel on the same principal surface of said substrate.
6. A piezoelectric vibration device according to claim 1 ,
wherein
each of said electrode pairs is configured by at least one interleaved electrode pair.
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Cited By (4)
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US20130083044A1 (en) * | 2011-09-30 | 2013-04-04 | Qualcomm Mems Technologies, Inc. | Cross-sectional dilation mode resonators |
US9099986B2 (en) * | 2011-09-30 | 2015-08-04 | Qualcomm Mems Technologies, Inc. | Cross-sectional dilation mode resonators |
US9270254B2 (en) | 2011-09-30 | 2016-02-23 | Qualcomm Mems Technologies, Inc. | Cross-sectional dilation mode resonators and resonator-based ladder filters |
CN109643981A (en) * | 2016-09-07 | 2019-04-16 | 罗伯特·博世有限公司 | Pass through the tunable lithium niobate resonator and filter of lithiumation and de- lithium |
Also Published As
Publication number | Publication date |
---|---|
JPWO2006046672A1 (en) | 2008-05-22 |
WO2006046672A1 (en) | 2006-05-04 |
US20080136542A1 (en) | 2008-06-12 |
DE112005002645T5 (en) | 2009-03-05 |
JP5052136B2 (en) | 2012-10-17 |
JP2012023756A (en) | 2012-02-02 |
US7893784B2 (en) | 2011-02-22 |
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