JP2001177346A - Piezoelectric oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize output frequency, without disturbing miniaturization of a surface mount type crystal oscillator and to enhance the latitude of designing a wiring pattern. SOLUTION: Circuit components 9 of an oscillation circuit 2 and a buffer amplifier circuit 23 or the like are mounted in the inside of a box-shaped printed circuit board (ceramic multilayer board) 2, and a crystal vibrator package 3 is overlapped on the printed circuit board 2 and integrated. A shield conductive film 11 is provided only at a part opposed to a part of a resonance circuit deciding an oscillating frequency of the oscillation circuit 22 among the circuit components 9 of the oscillation circuit 22, even in the inside of the printed circuit board 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric oscillator, and more particularly to a surface-mounted piezoelectric oscillator that can be used as a reference frequency source for a mobile communication device such as a mobile phone.

[0002]

2. Description of the Related Art A portable telephone terminal is required to be light and thin, and a crystal oscillator for generating a reference oscillation signal used therein is also required to be small and thin. In order to satisfy such demands for miniaturization and thickness reduction, piezoelectric oscillators in which an oscillation circuit, a temperature compensation circuit, and the like and a crystal oscillator are integrated have been conventionally provided.

However, in a crystal oscillator having such a structure, when the crystal oscillator is mounted on a motherboard of a set device such as a mobile phone terminal, a stray capacitance around the oscillation circuit is reduced by a wiring pattern of the motherboard or a device or circuit arranged near the motherboard. Not constant. Therefore, the oscillation frequency changes due to the stray capacitance, and the oscillation frequency of the crystal oscillator changes before and after mounting on the motherboard. Therefore, there is a problem that fine adjustment is required after mounting the piezoelectric oscillator.

Therefore, in the crystal oscillator disclosed in Japanese Patent Application Laid-Open No. 8-37421, the above-mentioned problem is solved by providing a shield layer on the entire mounting surface side of the multilayer structure substrate. However, in this crystal oscillator, since the shield layer is provided on the whole of the multilayer structure substrate, there is no space for providing the wiring electrodes connecting the upper surface and the lower surface of the multilayer structure substrate inside the multilayer structure substrate, and the crystal oscillator is not used. There was a problem that it hindered miniaturization.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to maintain a stable output frequency without hindering downsizing of a piezoelectric oscillator. An object of the present invention is to provide a piezoelectric oscillator that can be used.

For this reason, the piezoelectric oscillator according to claim 1 is
A piezoelectric oscillator including at least a piezoelectric vibrator, an oscillation circuit, and an amplifier circuit for amplifying an output of the oscillation circuit, wherein a first container accommodating the oscillation circuit and the amplifier circuit and a second container accommodating the piezoelectric oscillator. And the container is integrated with the conductive film for shielding only between the mounting surface and the portion of the resonance circuit that determines the oscillation frequency of the oscillation circuit among the circuit components constituting the piezoelectric oscillator and the oscillation circuit. It is characterized by being formed.

[0007] Here, the first container and the second container may be integrally formed, or may be separately formed and later joined and integrated. Further, the first container and the second container may be integrated so as to be vertically stacked, or the second container may be mounted on the upper surface of the first container, and may be arranged side by side. And may be integrated. Further, the shield conductive film may be grounded in an AC manner or in a DC manner.

In the piezoelectric oscillator according to the first aspect, a shielding conductive film is formed only between the mounting surface and the circuit components constituting the piezoelectric vibrator and the oscillation circuit at most. Wiring electrodes and circuit components can be provided between other circuit components (for example, circuit components constituting an amplifier circuit) and the mounting surface, thereby increasing the degree of freedom in wiring design and reducing the size of the piezoelectric oscillator. Can be planned. However, if the oscillation circuit and other circuits cannot be separated by an IC or the like, or if they are shared, the shield between the circuit components that make up the other circuits and the mounting surface is also required. A conductive film for use may be formed, and the effect of the present invention is not hindered thereby.

On the other hand, since the conductive film for shielding is formed at least between the portion of the resonance circuit that determines the oscillation frequency of the oscillation circuit and the mounting surface, the oscillation circuit is shielded by the conductive film for shielding on the mounting surface side. As a result, the output frequency of the piezoelectric oscillator can be stabilized.

[0010] The piezoelectric oscillator according to claim 2 is a piezoelectric oscillator according to claim 1.
In the piezoelectric oscillator described in the above, the second container is located on the first container, and an outer surface of the second container is covered with a shield plate.

According to the second aspect of the present invention, since the piezoelectric oscillator is shielded by the shield plate on the side opposite to the mounting surface, external noise such as radio waves can be cut off, and the output frequency can be further stabilized. it can.

According to a third aspect of the present invention, there is provided a piezoelectric oscillator according to the first aspect.
Alternatively, in the piezoelectric oscillator described in 2, the temperature compensation circuit for canceling the frequency temperature characteristics of the piezoelectric vibrator is housed in the first container.

[0013] Since the piezoelectric oscillator according to the third aspect has the temperature compensating circuit, the output frequency becomes stable against a temperature change.

According to a fourth aspect of the present invention, in the piezoelectric oscillator according to the first, second or third aspect, the first container is a laminated structure such as a laminated ceramic substrate or a laminated resin substrate. The shielding conductive film is formed inside a structure.

In the piezoelectric oscillator according to the fourth aspect,
Since the shielding conductive film is formed inside the first container made of the laminated structure, the shielding conductive film can be formed at a predetermined position, and the number of components can be reduced.

[0016]

FIG. 1 is a sectional view of a temperature-compensated crystal oscillator 1 according to an embodiment of the present invention.
FIG. 2 is a perspective view of the circuit board 2 on which circuit components are mounted. The crystal oscillator 1 has a structure in which a surface-mounted crystal resonator package 3 (hereinafter, referred to as a crystal resonator) is integrated on a circuit board 2 formed of a box-shaped ceramic multilayer substrate. By manufacturing the crystal unit 3 separately from the circuit side in this way, it is possible to reduce the variation in accuracy of the crystal unit 3 and increase the frequency accuracy. In addition, by laminating and integrating the crystal resonator 3 on the circuit board 2, the crystal resonator 3 also serves as a lid of the box-shaped circuit board 2, so that the number of components can be reduced and the crystal oscillator 1 can be reduced. Can be reduced in size.

First, the structure of the circuit board 2 will be described with reference to FIG. The circuit board 2 is formed of a ceramic multilayer board, has a concave portion 4 for mounting components in the center, and a wall portion 5 stands up around the concave portion 4. In the recess 4, a wiring pattern 10 made of a thick film conductor is formed by printing and baking a conductor paste. In addition, connection electrodes 7a and 7b made of a thick film conductor are also provided at four corners of the upper surface of the wall 5, and external electrodes 8 are also provided at four corners of the lower surface as shown in FIG. Connection electrodes 7a, 7b on upper surface
Is for connection to the crystal unit 3 and 2 of the 4
One electrode 7a is connected to the terminal electrode of the crystal piece 14, and the other two electrodes 7b are connected to the shield plate 15 and serve as ground electrodes. The external electrodes 8 on the lower surface are
Electrodes for connection when the crystal oscillator 1 is surface-mounted on a printed wiring board for equipment, etc., one for signal output, one connected to the power supply line, and the other two connected to the ground line Is done. Further, a printed resistor 6 is formed on the lower surface of the circuit board 2, and the lower surface of the circuit board 2 is covered with an insulating film at locations other than the external electrodes 8.

As shown in FIG. 1, a shielding metal layer 11 is laminated on a part of the circuit board 2 having a multilayer structure, and the shielding metal layer 11 is kept at the ground potential.
The connection electrodes 7a and 7b, the external electrode 8, the wiring pattern 10, and the wiring electrode 12 of the printed resistor 6 are connected to each other through a buried wiring 19 and a via hole 20 provided in the circuit board 2. The shielding metal layer 1
The embedded wiring 19 in the same plane as the metal layer 1
1 and at the same time.

The circuit board 2 includes circuits other than the crystal oscillator 3 among the circuits constituting the crystal oscillator 1.
For example, an oscillation circuit, a temperature compensation circuit, a buffer amplifier circuit, and the like are configured. Therefore, the surface mount type circuit components 9 constituting these circuits are mounted on the circuit board 2 by reflow soldering. For example, in the recess 4, transistors for oscillation and buffer amplification, varicaps, chip multilayer capacitors, temperature A chip thermistor (NTC thermistor) for compensation, a chip resistor, and the like are surface-mounted.

Next, as shown in FIG. 1, the AT-cut crystal blank 14 is housed in a case 13 having an upper surface opened, and one end is supported by the case 13. The entire upper surface of the case 13 is covered with a shield plate 15, and the crystal blank 14 is hermetically sealed in a package formed by the case 13 and the shield plate 15. Electrodes 17a and 17b are provided at the four corners of the lower surface of the case 13, two of which are connected to the terminal electrode of the crystal blank 14 via holes 16 and the other two electrodes 17b are connected to the via holes. It is electrically connected to the shield plate 15 through 16.

Thus, the connection electrode 7 on the upper surface of the circuit board 2
a and the electrode 17a on the lower surface of the crystal oscillator 3, the connection electrode 7b on the upper surface of the circuit board 2, and the electrode 17b on the lower surface of the crystal oscillator 3 are reflow soldered. As a result, the connection electrodes 7a and 7b of the circuit board 2 and the electrode 17 of the crystal unit 3
a and 17b are electrically connected by solder 18, and the circuit board 2 and the crystal unit 3 are mechanically connected.

FIG. 3 is a circuit diagram showing the configuration of the temperature compensated crystal oscillator 1 as described above. The crystal oscillator 1 includes a temperature compensation circuit (compensation voltage generation circuit) 21, a crystal oscillator 3,
It comprises an oscillation circuit 22 and a buffer amplifier circuit 23. The temperature compensation circuit 21 changes the output voltage applied to the crystal unit 3 according to the change in the ambient temperature,
It stabilizes the frequency by canceling out the frequency-temperature characteristic of the crystal unit 3, and is composed of a resistor, an NTC thermistor, and the like. Alternatively, a "conversion table" of the temperature versus the generated voltage recorded in the PROM is addressed by the output of a temperature sensor (not shown), taken out as digital data, and digitally processed as necessary. A signal that is extracted as a voltage signal by a DAC (DAC) may be used.

The oscillation circuit 22 is constituted by a Colpitts oscillation circuit having a common emitter. That is, in the oscillation circuit 22, a transistor 25 connected between the base and the emitter by the capacitor 24 and four resistors 2
6, 27, 28, 29 and a capacitor 30 constitute a Colpitts type. Only a DC component of the power supply voltage Vcc is applied to the collector of the transistor 25 by the resistor 26 and the capacitor 33, and the emitter is grounded via the resistor 27. The power supply voltage V is divided by the voltage dividing resistors 28 and 29.
cc is applied to the base with a partial pressure. In the oscillation circuit 22, a variable capacitance diode 31 is connected from the ground to the terminal electrode of the crystal unit 3,
The output voltage of the temperature compensation circuit 21 is input to the crystal unit 3 via the resistor 32.

The portion of the resonance circuit that determines the oscillation frequency of the oscillation circuit 22 is the portion that is obtained by removing the crystal resonator 3 from the portion surrounded by the broken line α in FIG.
29, capacitors 24 and 30 are included, and a resistor 32, a variable capacitance diode 31, and a transistor 25 are partially included. In order to stabilize the output frequency of the crystal oscillator 1,
A shielding metal layer 11 is formed at least on the lower surface side (mounting surface side) of a circuit component that is a part of the resonance circuit. Further, even when the shielding metal layer 11 is provided in a wider range, the upper limit of the range is almost equal to the oscillation circuit 2.
2 is a region facing the circuit components constituting the second component. On the other hand, the crystal resonator 3 surrounded by the broken line α is covered with the shield plate 15 on the upper surface side.

The buffer amplifier circuit 23 has a power supply voltage Vcc input to the collector via a resistor 35, an emitter grounded via a resistor 36 and a capacitor 37, and a voltage dividing resistor 3
The power supply voltage Vcc is divided at 8 and 39 to constitute a transistor 34 applied to the base.

Then, the quartz oscillator 3 is oscillated by the Colpitts-type oscillation circuit 22 with the emitter grounded, and the quartz oscillator 3
Is controlled by the voltage applied to the variable capacitance diode 31 to control the oscillation frequency. The oscillation output is taken out from the collector of the transistor 25, amplified by the next-stage grounded buffer amplification circuit 23, and output from the collector of the transistor 34. The fluctuation of the output frequency due to the temperature is corrected by the temperature compensation circuit 21.

In the crystal oscillator 1, the oscillation circuit 2
2 is a shielding metal layer 11 on at least a part of the mounting surface side.
, The output frequency can be stabilized. Further, since the outer surface side of the crystal unit 3 is also shielded by the shield plate 15, external noise can be cut off and the output frequency can be stabilized. In addition, since the shielding metal layer 11 is not provided in a region other than the oscillation circuit, the number of circuit wiring portions for forming the buried wiring 19 and the via hole 20 can be increased, and the degree of freedom in wiring design increases. In addition, since the shield portion is reduced, the wiring can be concentrated on the vacant portion of the circuit board 2 and the size of the temperature-compensated piezoelectric oscillator 1 can be reduced. In particular, in a temperature-compensated piezoelectric oscillator, the area of the circuit part that really needs a shield is smaller than the other parts,
The difference from the case where the entire surface is shielded becomes remarkable.

(Second Embodiment) FIG. 4 shows a temperature compensated crystal oscillator 4 using inverter elements 42 and 46.
1 represents the configuration. In the oscillation circuit 22 of the crystal oscillator 41, the inverter element 42 and the crystal oscillator 3
And the resistor 43 are connected in parallel, and the input side and the output side of the inverter element 42 are grounded via the capacitors 44 and 45. The inverter element 42 has a resistor 32
The output voltage of the temperature compensation circuit 21 is applied via a capacitor 48, and the variable capacitance diode 31 is connected between the ground and the input side of the inverter element 42 (or the crystal unit 3).

The output of the inverter element 42 is output through the buffer amplifier circuit 23 including the inverter element 46 and the capacitor 47. Here, the inverter element 46 constitutes a part of the oscillation circuit 22 and also constitutes a part of the buffer amplifier circuit 23.

In this example, a part of the resonance circuit that determines the oscillation frequency of the oscillation circuit 22 is obtained by removing the piezoelectric vibrator 3 from the part surrounded by the broken line α in FIG. And the inverter element 4
6, the capacitors 44 and 45, the resistor 32, and the variable capacitance diode 31 are partially included, and the shielding metal layer 11 is provided in the circuit board 2 so as to face these circuit components.

(Third Embodiment) FIG. 5 shows the configuration of still another crystal oscillator 51. This crystal oscillator 5
1, the transistor 5 of the Colpitts oscillation circuit 22
3 and the transistor 58 of the buffer amplifier circuit 23 are connected in series to the power supply. That is, in the oscillation circuit 22, the emitter of the transistor 53, whose base and emitter are coupled by the capacitor 52, is grounded via the resistor 54 and the capacitor 55, and the trimmer capacitor 56 is connected to the input side of the crystal resonator 3. The output side of the crystal resonator 3 is connected to the base of the transistor 53.

In the buffer amplifier circuit 23, the power supply voltage Vcc is applied to the collector of the transistor 58 via the resistor 63, and the AC noise of the power supply voltage Vcc is released to the ground by the capacitor 61. The transistor 58 is connected between the collector and the base by a resistor 59, and the base is grounded via a capacitor 60.
Further, the base of the transistor 58 is connected to the base of the transistor 53 of the oscillation circuit 22 via a resistor, and the emitter of the transistor 58 is cascade-connected to the collector of the transistor 53 of the oscillation circuit 22. The output of the buffer amplifier circuit 23 is extracted from the collector of the transistor 58 via the capacitor 62.

In this example, the part of the resonance circuit that determines the oscillation frequency of the oscillation circuit 22 is obtained by removing the piezoelectric vibrator 3 from the part surrounded by the broken line α in FIG. The circuit board 2 includes a trimmer capacitor 56, a capacitor 55, and resistors 54 and 57.
A shielding metal layer 11 is provided therein.

(Fourth Embodiment) FIG. 6 is a sectional view showing the structure of a crystal oscillator 61 according to still another embodiment of the present invention. The crystal oscillator 61 is an integrated circuit board and a case on the side of a crystal oscillator, and uses a ceramic package 62 having concave portions 63 and 64 on the upper surface and the lower surface, respectively. The crystal blank 14 is accommodated in the concave portion 63 on the upper surface of the package 62, and the upper surface opening of the concave portion 63 is closed with the shield plate 15 to constitute the crystal resonator 3. A wiring pattern is formed on the top surface of the concave portion 64 on the lower surface of the package 62, and the circuit components 9 constituting the oscillation circuit 22, the temperature compensation circuit 21, the buffer amplifier circuit 23, and the like are surface mounted on the top surface of the concave portion 64. Have been. The lower surface opening of the concave portion 64 is covered with a ceramic lid 65, and electrodes 8 are provided at four corners of the lower surface of the lid 65. A metal layer 11 for shielding is formed on the upper surface or inside of the lid 65, and is directly below a resonance circuit portion (for example, a portion α in FIGS. 3 to 5) in the circuit components 9 constituting the oscillation circuit 22. Is covered with the shielding metal layer 11. Further, a wiring pattern can be formed on the upper surface of the lid 65 as necessary, and the circuit component 9 can be mounted.

With the crystal oscillator 61 having such a structure, the same effects as those of the crystal oscillator 1 having the structure as shown in FIG. 1 can be obtained, and the output frequency can be stabilized while the size of the crystal oscillator 61 can be reduced. Also, the degree of freedom of the wiring pattern can be increased.

The type of the crystal oscillator may be any type. For example, a temperature-compensated crystal oscillator (TCXO) to which a temperature compensation circuit is added as described above, a crystal oscillator without temperature compensation (SPXO), or a voltage-controlled crystal oscillator (VCXO) may be used.

[0037]

According to the piezoelectric oscillator of the present invention, the output frequency can be stabilized without hindering downsizing of the piezoelectric oscillator.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a temperature-compensated crystal oscillator according to an embodiment of the present invention.

FIG. 2 is a perspective view of a circuit board used in the crystal oscillator according to the first embodiment.

FIG. 3 is a circuit diagram of the crystal oscillator according to the first embodiment;

FIG. 4 is a circuit diagram of a temperature-compensated crystal oscillator using an inverter element.

FIG. 5 is a circuit diagram of yet another crystal oscillator.

FIG. 6 is a cross-sectional view of a temperature-compensated crystal oscillator according to yet another embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 temperature-compensated crystal oscillator 2 circuit board 3 crystal oscillator 9 circuit component 11 shielding metal layer 14 crystal piece 15 shield plate 19 embedded wiring 21 temperature compensation circuit 22 oscillation circuit 23 buffer amplification circuit 62 package 63, 64 recess 65

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Mitsuhiro Murata 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Stock Company Murata Manufacturing Co., Ltd. (72) Inventor Makoto Fujita 2-26-10 Tenjin, Nagaokakyo-shi Kyoto Prefecture Stock Company F-term in Murata Manufacturing (reference) 5E321 AA02 AA17 BB21 GG05 5J020 BD01 BD04 5J079 AA04 BA39 BA43 FA02 FA13 FA14 FA21 FB03 GA02 GA04 GA09 HA07 HA09 HA15 HA28 HA29 KA05

Claims (4)

[Claims] At least a piezoelectric vibrator, an oscillation circuit,
In a piezoelectric oscillator including an amplifier circuit for amplifying the output of the oscillation circuit, a first container accommodating the oscillation circuit and the buffer amplifier circuit and a second container accommodating the piezoelectric vibrator are integrally formed. The shield conductive film is formed only between the mounting surface and at least the portion of the resonance circuit that determines the oscillation frequency of the oscillation circuit among the circuit components forming the piezoelectric vibrator and the oscillation circuit. Piezoelectric oscillator. 2. The piezoelectric device according to claim 1, wherein the second container is located on the first container, and an outer surface of the second container is covered with a shield plate. Oscillator. 3. The piezoelectric oscillator according to claim 1, wherein a temperature compensation circuit for canceling frequency temperature characteristics of the piezoelectric vibrator is housed in the first container. 4. The method according to claim 1, wherein the first container is a laminated structure such as a laminated ceramic substrate or a laminated resin substrate, and the conductive film for shielding is formed inside the laminated structure. The piezoelectric oscillator according to claim 1, 2 or 3.