JPH0637583A - Two-port saw resonator - Google Patents

Abstract

PURPOSE:To improve stability in a way of making a resonance frequency remarkably variable by comprising a two-port SAW resonator by letting second and third comb-line electrodes arranged on both sides of a first comb-line electrode share a function of the reflector of a surface acoustic wave. CONSTITUTION:After a metallic conductor such as an Al, an Au, etc., is filmed on the plane of a piezoelectric plate 100 to which mirror polishing processing is applied, fine patterns are formed on first to third comb-line electrodes 103-108 by using a means of photolithography, etc. In the two-port SAW resonator, the size and arrangement of the electrode are decided so that the conductor arranging period PR of the second and third comb-line electrodes 105-108 can be set at almost 1/2 of the wavelength of a generated surface acoustic wave. Also, a ratio of conductor width to conductor interval is set at around 1. Meanwhile, the conductor arranging period PT of the first comb-line electrodes 103, 104 is set so as to let the frequency to impart the maximum value of radiant conductance characteristic provided at the first comb-line electrodes 103, 104 almost coincide with the one to impart the maximum value of reflection characteristic generated by the second and third comb-line electrodes 105-108.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-port SAW resonator electrode structure using surface acoustic waves.

[0002]

2. Description of the Related Art A conventional electrode structure of a two-port SAW resonator is described in, for example, U.S. Pat. No. 3,886,504 or JP-A-61-281612. All of these detect the surface acoustic wave by exciting it. 2
It consists of three comb electrodes and grating reflectors arranged on both sides of the electrodes.

[0003]

However, the above-mentioned prior art has a problem that it is not sufficient for the purpose of obtaining a sufficient frequency variable range by using it in the voltage controlled crystal oscillator. Therefore, the present invention solves such a problem, and an object of the present invention is to make a 2-port SAW resonator having a frequency variable width several times wider than that of a conventional one by using a crystal substrate to produce VHF and UHF bands. It is to provide the market with a voltage controlled crystal oscillator that can be used directly.

[0004]

Two-port SAW of the present invention
The resonator includes (1) a first comb-teeth electrode that excites a surface acoustic wave on a piezoelectric flat plate, and the first comb-shaped electrode in the propagation direction of the surface acoustic wave.
The second and third comb-teeth electrodes are arranged as reflectors on both sides of the comb-teeth electrode, and the first comb-teeth electrode described in (2) and (1) is used as an input port, and the second and third comb-teeth electrodes are arranged. Connect the three comb-teeth electrodes to each other to make an output port, (3)
The material of the piezoelectric flat plate described in (1) is quartz and the cut angle is ST cut, and the material of the piezoelectric flat plate described in (4) (1) is quartz and the cut angle is LST cut. , (5) The voltage controlled oscillator is configured by connecting the input port side of the 2-port SAW resonator described in (2) to the amplifier input side of the oscillation circuit and connecting at least the variable capacitance diode to the output port side. To do.

[0005]

By configuring the reflector by connecting the load impedance between the electrodes of the comb-teeth electrode on the detection side, the phase of the reflected wave of the surface acoustic wave can be varied by changing the magnitude of the load impedance. The resonance frequency of the 2-port SAW resonator can be changed significantly.

[0006]

EXAMPLES Examples of the present invention will be described below in order.

First, FIG. 1 shows a 2-port SA of the present invention.
It is a top view which shows the Example of the electrode structure which a W resonator has. The names of the parts in FIG. 1 are as follows. Reference numeral 100 denotes a piezoelectric plate, which is made of a piezoelectric material such as quartz, LiTaO ₃ , and LiNbO ₃ . Reference numeral 101 is an input signal power source, 102 is a load impedance connected to the output side, and 103 and 104 are first comb-teeth electrodes, which are applied bi-directionally orthogonal to the comb-teeth electrodes by applying the AC voltage of 101. Exciting propagating surface acoustic waves. Second comb electrodes 105 and 106 are connected to the load impedance 102. 1
Reference numerals 07 and 108 denote third comb-teeth electrodes, which are also connected to the load impedance. The first and second comb-teeth electrodes serve as a reflector for reflecting the surface acoustic waves generated by the first comb-teeth electrode to realize a resonance phenomenon.

Explaining the details of the structure in more detail, the above-mentioned first to third comb-teeth electrodes are formed of Al, Au, A on the surface of the piezoelectric flat plate 100 which is mirror-polished.
After forming a metal conductor such as g and Cn by a film forming means such as vapor deposition and sputtering, a fine pattern is formed by using a means such as photolithography. 2-port SA of the present invention
In the W resonator, the dimensions and arrangement of the electrodes are configured as follows. First, the conductor arrangement period P _{R of} the second and third comb-teeth electrodes
Is approximately half the wavelength λ of the surface acoustic wave that is generated. Further, it is preferable that the ratio 1 / s of the conductor width 1 and the conductor interval s is approximately 1.

On the other hand, the conductor arrangement period P _{T of} the first comb tooth electrode
Is set so that the frequency giving the maximum value of the radiative conductance characteristic of the comb electrode of 1 etc. is substantially the same as the frequency giving the maximum value of the reflection characteristic made by the second and third comb tooth electrodes. . Further, when the conductor width of the first comb tooth electrode is 1 and the conductor spacing is s, the spacing between the first and second comb tooth electrodes and the spacing between the first and third comb tooth electrodes are set to s. The l / s ratio may be 1 or less, but l / s ≧ 1 is advantageous because it can reduce the equivalent series resistance of the 2-port SAW resonator.

Also, the logarithmic ratio of the first and second comb electrodes and the first and third comb electrodes is M / N = 0.2 where M is the first and N pairs are the second and third comb electrodes. It is better to set it to ~ 1. The electrode film thickness varies depending on the material of the piezoelectric flat plate 100 and the cut angle azimuth, but it is ST cut and LST cut of crystal,
If the electrode metal is mainly Al, the ratio H / λ of the electrode film thickness H and the wavelength λ of the surface acoustic wave is preferably set to about 0.01 to 0.03. At this time, the cutting angle of the ST cut and the cutting direction of the LST cut are set so that the optical axis of the crystal is counterclockwise in the ST cut so that the first-order temperature coefficient of the frequency-temperature characteristic becomes zero near room temperature. A Y plate rotated around 30 ° to 35 ° + X axis is used, and in the LST cut, a mechanical axis of the crystal is a Z plate rotated counterclockwise around 9 ° to 15 ° + X axis. The two-port SAW resonator of the present invention obtained by the above configuration has the first comb-teeth electrode as an input terminal (1 and 1'in FIG. 1) and the second and third comb-teeth electrodes as an output terminal (see FIG. The terminal arrangement of 1 and 2 and 2 ') can be taken as a line.

Next, FIG. 2 is a circuit diagram showing an equivalent circuit of the 2-port SAW resonator of the present invention. The names of the parts in the figure are as follows: 201 is the input signal power source, 202 is the parallel capacitance created by the first comb-teeth electrode, 203, 204, and 205 are equivalent constants in the resonance state of the 2-port SAW resonator. Therefore, 203 is an equivalent series inductance, 204 is an equivalent series capacitance, and R of 204 is an equivalent series resistance. 20 more
C _O of 6 is a parallel capacitance formed by the second and third comb-teeth electrodes described above. C _L of 207 indicates a state of connecting the capacitance as a load impedance above. In the figure, 1 and 1'indicate the input terminal side and 2 and 2'indicate the output terminal side. The 2-port SAW resonator viewed from the input signal power source of 201 exhibits the same characteristics as the 1-port crystal resonator in which the load capacitance C _L is connected in series to the resonator arm. This state is shown in FIG.

In the figure, the horizontal axis is the load capacitance C _L value,
The vertical axis represents the relative value of the resonance frequency viewed from the input terminal side of the 2-port resonator, and the curve 301 in the figure is the Δf / f vs. C _L characteristic curve of the conventional 1-port SAW resonator. A curve 302 is a 2-port S of FIG. 1 which is an embodiment of the present invention.
The characteristics are the same as those of the AW resonator. The large difference between the two can be explained by the following reasons. First, since all the comb-teeth electrodes detect the electric charges generated by the surface acoustic waves, the equivalent series capacitance value C of FIG. 2 can be made large.

Secondly, since the reflector having the reactance load connected to the second and third comb-teeth electrodes is constructed, the load _CL
This is because the reflection characteristic changes depending on the size of the and the resonance frequency changes. Then finally, the 2-port SA of the present invention
A voltage-controlled oscillator using a W resonator (hereinafter simply referred to as V
(Called CXO). FIG. 3 is a circuit diagram of an embodiment in which the 2-port SAW resonator of the present invention is a VCXO. The name of each part in the figure is 400, which is a control signal voltage source for the VCXO and generates a DC voltage Vc.

Reference numeral 401 is an input terminal of the control voltage to the VCXO, 402 is a resistor, 403 is a variable capacitance element, and 404 and 4
08 and 409 are capacitors, 406 and 407 are resistors for setting the DC operating point of the transistor 410, 410 is a transistor, 411 is a DC power source, 412 is a VCXO output signal terminal, and 413 is a resistor that sets the collector current of the transistor 410. Is. Finally, 405 is 2 of the present invention.
In the port SAW resonator, terminals 1 and 1'are connected to the transistor circuit side and 2 and 2'are connected to the variable capacitance element side.

Transistor 4 at 1 and 1'terminals of 405
The entire circuit including 10 constitutes the amplification circuit of the Colpitts type oscillation circuit. The reason why the oscillation circuit of FIG. 3 becomes a VCXO can be explained as follows. The equivalent capacitance value of the variable capacitance element 403 increases or decreases depending on the magnitude of the control voltage Vc. As a result, the series connection capacitance value of the capacitor 404 and the capacitor made by 403 described above, that is, the load capacitance C _L of the 2-port SAW resonator changes. As a result, the resonance frequency of the 2-port SAW resonator 405 changes as described in FIG. Then, the oscillation frequency of the oscillation circuit can be changed, and the VCXO is obtained. In particular, the VCXO using the 2-port SAW resonator of the present invention using the crystal ST cut and the LST cut is excellent in that the frequency variation with temperature change and the Q value are high and stable.

[0016]

According to the present invention, the second and third comb-teeth electrodes arranged on both sides of the first comb-teeth electrode for exciting the surface acoustic wave also serve as a surface acoustic wave reflector. Port SA
Since the W resonator is configured, the resonance frequency of the two-port SAW resonator can be significantly changed as compared with the conventional one due to the change of the load impedance, and the frequency stability such as ST cut and LST cut of the crystal is high. Since the 2-port SAW resonator can be configured, it is possible to provide the voltage controlled oscillator with excellent stability to the market.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a 2-port SAW resonator of the present invention.

FIG. 2 is a circuit diagram showing an equivalent circuit in one embodiment of the 2-port SAW resonator of the present invention.

FIG. 3 is a characteristic diagram showing a change in a relative value of a resonance frequency with respect to a load capacitance.

FIG. 4 is a circuit diagram showing a circuit configuration of a voltage controlled oscillator including a 2-port SAW resonator of the present invention.

[Explanation of symbols]

 100 ... Piezoelectric flat plate 103, 104 ... First comb tooth electrode 105, 106 ... Second comb tooth electrode 107, 108 ... Third comb tooth electrode 101 ... Input signal power source 102 ... Load impedance

Claims (5)

[Claims] 1. A first comb-teeth electrode for exciting a surface acoustic wave on a piezoelectric flat plate, and a second comb and a third comb on both sides in the propagation direction of the surface acoustic wave and parallel to the first comb-teeth electrode. 2-port SA, characterized by arranging the comb-teeth electrode as a reflector
W resonator. 2. The two-port SAW resonator according to claim 1, wherein the first comb-teeth electrode serves as an input port, and the second and third comb-teeth electrodes are connected to each other to serve as an output port. . 3. The two-port SAW resonator according to claim 1, wherein the material of the piezoelectric flat plate is quartz and the cut angle is ST cut. 4. The two-port SAW resonator according to claim 1, wherein the piezoelectric flat plate is made of quartz and the cut angle is LST cut. 5. A two-port SAW resonator according to claim 2, wherein the input port side is connected to the amplifier input side of the oscillation circuit and at least the variable capacitance diode is connected to the output port side to form a voltage controlled oscillator. .