JPH05160665A - 2-port saw resonator - Google Patents

Abstract

PURPOSE:To provide a resonator of high frequency stability by resolving the problem that the resonance condition is changed to make the resonance phenomenon unstable by the terminal condition of the output port of a two-port SAW resonator. CONSTITUTION:An input IDT 113 and an output IDT 114 are connected with a connection conductor 112 between them and are arranged between a pair of reflectors 107, 108 on a piezoelectric body plane plate 100. The arrangement period ((conductor width lR) + (conductor interval SR)) of conductor strips of each reflector is set to about 1/2 of a surface acoustic wave to be generated, and 1R/SR is set to about one. The conductor arrangement period ((conductor width lr) + (conductor interval dr)) of input and output IDTs is so set that the frequency which gives a maximum value of reflection characteristics of the surface acoustic wave generated by the reflector coincides with the maximum value of radiation conductance characteristics of IDTs. The energy confinement type SAW resonator where the total reflection coefficient obtained by unifying total logarithms of IDTs is >=0.8 is constituted to make the two-port SAW resonator.

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, US Pat. No. 3,886,504 or JP-A-61-281612. These both excite and detect surface acoustic waves. 2
It consists of two comb-shaped transducers (hereinafter referred to as IDTs) and grating reflectors arranged on both sides thereof.

[0003]

However, in the above-mentioned prior art, the two-port SAW resonator is incorporated in the oscillation circuit and the S
In realizing the AW oscillator, there is a problem that the resonance condition of the 2-port resonator is likely to change and the resonance phenomenon tends to become unstable depending on the termination condition of the output (detection) port of the 2-port SAW resonator. Therefore, the present invention solves such a problem, and an object of the present invention is to produce a two-port SAW resonator having excellent resonance stability to bring a UHF band SAW oscillator having excellent frequency stability to the market. To provide.

[0004]

Two-port SAW of the present invention
The resonator is (1) a 2-port S in which an IDT that excites a surface acoustic wave is sandwiched between a pair of reflectors on a piezoelectric plate.
In the AW resonator, the reflector and the IDT are formed by periodically arranging metal conductor strips.
The distance between the strips closest to each other corresponds to the line-to-space space of the IDT, and the frequency that gives the maximum radiative conductance of the IDT and the reflection center frequency of the reflector are made to substantially coincide with each other.
After constructing a so-called energy confinement type SAW resonator having a total reflection coefficient Γ of 0.8 or more, the IDT is alternately input from the reflector side with an input IDT, an output IDT or an output IDT, and an input IDT. It is divided into two or more parts, (2) the line-to-space ratio of the reflector is almost 1, and the line-to-space ratio of the IDT is 1 or more, (3) the ground of the input and output IDTs. The connecting conductor connecting the electrode fingers belonging to the potential side across the propagation path of the surface acoustic wave is an integral multiple of the line width of the IDT, and the space on both sides of the connecting conductor is an integral multiple of the space width of the IDT. Is characterized in that

[0005]

1 is a plan view showing an embodiment of an electrode structure of a 2-port SAW resonator according to the present invention. The configuration of the present invention will be described in detail with reference to FIG. First, the names of the respective parts in FIG. 1 are listed. 100 is a piezoelectric plate, 101 is an AC power supply, 102 and 103 are input terminals of a 2-port SAW resonator, 104 and 105 are output terminals, and 106 is an output terminal. The resistors 107 and 108 are connected in parallel to each other and serve as terminal loads, 107 and 108 are reflectors (grating reflectors) in which a large number of metal conductor strips are arranged in parallel and both ends are connected, and 109 and 110 are IDs.
T is a ground potential side conductor, 112 is a connection conductor, 113 is an input side IDT, and 114 is an output side IDT.

The piezoelectric flat plate of 100 is made of quartz or LiTaO.
The surface of a piezoelectric material represented by ₃ , LiNbO ₃ , etc. is used as a mirror-polished finish state. The AC power source 101 is connected to the positive electrode and the negative electrode of the excitation IDT to generate a surface acoustic wave (SAW). The terminating load resistance of 106 represents the input impedance of a transistor connected to the output end of the 2-port SAW resonator. The conductor patterns 107 and 108, 113, 112, 114, etc. are formed on the 100 by forming a metal thin film of Al, Au, Ag, Cu, etc. by means such as vapor deposition or sputtering, and then finely forming it by means such as photolithography. It is formed by forming a pattern. In the two-port SAW resonator of the present invention, the reflectors 107 and 108 and the IDT are made into the following one-port SAW resonator and then modified. First reflector 1
The arrangement period P _R of the conductor strips 07 and 108 is approximately 1/2 of the wavelength λ of the generated surface acoustic wave (P in FIG. 1).
_{R = S R + l R)} . Further, the ratio l _R / S _R between the conductor width l _R and the conductor spacing S _R is set to approximately 1. On the other hand, the conductor array period P _T of the IDT is set so that the frequency giving the maximum value of the reflection characteristic of the surface acoustic wave created by the reflector and the maximum value of the radiation conductance characteristic of the IDT match (P in FIG. 1). _T
= L _T + S _T. ) For example, the piezoelectric plate 100 is S
It is a T-cut crystal plate and the reflector and IDT conductor metal is A
When it is 1, the ratio of P _R and P _T is P _R / P
_T = 1.002 to 1.02. Furthermore also the distance between the IDT conductor width l _T and the conductor as S _T, constitute a one-port SAW resonator a distance between the most closely spaced conductors of the reflector and IDT are set to be the S _T. or,
The ratio of l _T / S _T may be 1 or less, but if it is 1 or more,
The series resonance resistance of the 1-port SAW resonator can be reduced. Furthermore, the 1-port SAW resonator is an integral IDT.
The ratio M / N of the total logarithm M of M to the number N of conductors of the reflector is 1.0 to
In addition to the maximum Q value of 2.0, the ID integrated when the positive electrode and the negative electrode of the IDT are paired into M pairs
A so-called energy confinement type SAW resonator in which the total reflection coefficient Γ of T is defined as follows and 0.8 or more is realized.

[0007]

[Equation 1]

Here, M is the IDT logarithm, and a is the electrode 1.
The reflection coefficient of the surface acoustic wave per line, H is the conductor film thickness, and λ is the wavelength of the surface acoustic wave. For example, in the case of an IDT formed of an Al conductor with the ST cut quartz plate, a 1-port SAW resonator having a sufficiently good Q value can be constructed if M is 80 or more. At this time, Γ = 2.448. In the two-port SAW resonator of the present invention, the IDT electrode of the above-mentioned one-port SAW resonator is divided into a plurality of input and output IDTs while keeping the electrode coordinate arrangement as it is, and is then connected to the ground potential side. 2-port SAW by connecting electrode groups with connecting conductors
It constitutes a resonator. As a result of prototyping the method of dividing the IDT under various conditions and examining the stability of the resonance frequency, it is better that the number of input and output IDTs is a plurality of two or more, and the arrangement is , The input IDTs, the output IDTs, the input IDTs, ... Or the inverses of the output IDTs, the input IDTs, the output IDTs. At this time, as described above, the position coordinate of the electrode finger of the IDT maintains the position of the above-mentioned 1-port SAW resonator. Next, a large number of IDTs divided in this way
After connecting the electrode fingers belonging to the ground side of the conductors 109, 110, etc., 109, 110, etc. are further connected to each other by using the connection conductor 112 formed across the propagation path of the surface acoustic wave. This connecting conductor is formed by shifting the positions of the original electrode fingers to the left and right so as to maintain the electrode finger positions of the IDT when formed as a 1-port SAW resonator, The width of the connecting conductor is the line width l of the IDT
The size of nl _T is an integral multiple of _T , and the spaces existing on both sides of the connecting conductor have an integer multiple mS _T and kS _T of the space width S _T of the IDT. (However, the above n, m, and k are integers).

Next, the second aspect of the present invention obtained by the above configuration
The resonance characteristics (transmission characteristics) of the port SAW resonator are shown in FIG. The 2-port SAW resonator shown in FIG. 2 is composed of two reflectors, four input IDTs and three output IDTs, and has a resonance frequency of 130 MHz. The horizontal axis in FIG. 2 represents frequency, and the vertical axis represents operating attenuation amount S _B (201) and transmission phase amount (202) φ in the same figure. In the example of FIG. 2, the in-phase type in which φ changes ± 90 ° around 0 ° is shown, but the reverse-phase type in which φ changes ± 90 ° around 180 ° also shows how to connect the input IDT and the output IDT. It can be realized by adding.

[0010]

As described above, according to the present invention, in the two-port SAW resonator, the input I for exciting the surface acoustic wave is generated.
Since many DTs are evenly distributed in the longitudinal direction of the resonator, the degree to which the electrode fingers of the output IDT reflect the surface acoustic waves with respect to some changes in the termination load condition of the output IDT. Since the resonance amplitude does not change greatly even if the frequency changes a little, the stable resonance phenomenon can be maintained and the frequency stability can be realized by using the oscillator in the UHF band.

[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 characteristic diagram showing transmission characteristics of a 2-port SAW resonator according to the present invention.

[Explanation of symbols]

 100 Piezoelectric plate 107, 108 Reflector 113 Input IDT 114 Output IDT 112 Connection conductor 101 AC power supply 106 Termination load resistance

Claims (3)

[Claims] 1. A 2-port SAW in which an IDT for exciting a surface acoustic wave is sandwiched between a pair of reflectors on a piezoelectric flat plate.
In the resonator, the reflector and the IDT are formed by periodically arranging metal conductor strips, and the distance between the closest strips of the reflector and the IDT corresponds to the line-to-space space of the IDT. The so-called energy confinement type SAW resonator in which the frequency that gives the maximum radiative conductance of the IDT and the reflection center frequency of the reflector are made to substantially match, and the total reflection coefficient Γ of the IDT is 0.8 or more. And configure the ID
T is input IDT, output IDT or output ID from the reflector side
A two-port SAW resonator characterized in that it is divided into two or more pieces each of which is alternately arranged with T and an input IDT. 2. The two-port SAW resonator according to claim 1, wherein the line-to-space ratio of the reflector is approximately 1 and the line-to-space ratio of the IDT is 1 or more. 3. The connection conductor connecting electrode fingers belonging to the ground potential side of the input and output IDTs across the propagation path of the surface acoustic wave is an integral multiple of the line width of the IDT and both sides of the connection conductor. 2. The two-port SA according to claim 1, wherein the space is a multiple of the space width of the IDT.
W resonator.