JPS63119310A - Surface acoustic wave resonator - Google Patents

Abstract

PURPOSE:To extend the frequency range between the resonance frequency and the frequency for the occurrence of longitudinal mode spurious by setting shapes of interdigital electrodes and grating reflectors to satisfy a specific condition. CONSTITUTION:A ratio P/L of a period pitch P of grating reflectors 22 and 23 to an electrode period L of interdigital electrodes 24 formed on the surface of a piezoelectric substrate 21 by vapor-deposition satisfies the condition expressed with a formula where epsilon is a reflection ratio. Distances between interdigital electrodes 24 and grating reflectors 22 and 23 are so set that a resonance point fr of a resonator and a center frequency fo of the reflection coefficient frequency characteristic of grating reflectors satisfy relations 1.1 fo<=fr<=2.0fr. Thus, the interval between the resonance peak of the surface acoustic wave resonator and the longitudinal mode spurious is extended, and the frequency variable width is extended when it is used in a voltage controlled oscillator.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a surface acoustic wave resonator for a voltage-controlled oscillator, and in particular to a surface acoustic wave resonator that allows a voltage-controlled oscillator to greatly expand the oscillation frequency variable range. Concerning children.

[Conventional technology]

Conventionally, the characteristics of this type of surface acoustic wave resonator are as shown in FIG. Set to the center frequency fO. Each electrode and reflector is formed as a metal film pattern on the piezoelectric substrate, and the mechanical impedance ratio of the patterned metal film to the piezoelectric substrate is z = 1 + 8 (e is the reflection ratio).
Then, the Q of the resonator? In order to increase the height, the conditions for the periodicity of the interdigital electrodes and the periodic pitch PP, -1 of the crating reflector are generally set as r-Σ(10-'). Optimization of quartz SAW resonator structure
tzSAW reaonator 5structure
with groove grating) K has been proposed.

[Problem that the invention seeks to solve]

The resonance characteristics of the conventional surface acoustic wave resonator described above, as shown in FIG. 5, have a resonance point at the center of the reflection coefficient frequency characteristics of FIG. 4, and therefore can be said to be the optimum conditions for a resonator. When this surface acoustic wave resonator is used in a voltage controlled oscillator, the oscillation frequency is lower than the resonant frequency and changes depending on the voltage, but the oscillation frequency variable width is limited by the longitudinal mode spurious 8 shown in Figure 5. However, the disadvantage is that the variable range is narrow.

An object of the present invention is to provide a surface acoustic wave resonator in which the frequency range between the resonant frequency and the frequency at which longitudinal mode spurious occurs is widened.

[Means for solving problems]

The surface acoustic wave resonator of the present invention has a grating reflector period (1+zs!−) with respect to the electrode period LK of the interdigital electrodes.
! - Rideme), and the resonance point of the resonator (period π wave number) frt - For the center frequency fO of the reflection coefficient frequency characteristic of the grating reflector, Llfo≦fr≦! Ofr
The distance between the interdigital electrode and the grating reflector is set so that

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of the present invention.

In the figure, a piezoelectric substrate 21 has 11 interdigital poles 2 on its surface.
4 and the conductor patterns of the crating reflectors 22 and 23 are formed by vapor deposition. Although the structure of the surface acoustic wave resonator shown in FIG. 1 is similar to the conventional ID5itLa surface wave resonator, the feature of FIG.
Greig Ink Reflector for % Polarization 22.230
If the periodic pitch PO ratio r is 1 (1+L17≦℃≦T (1+L5T), and the resonance point frf of the resonator is the center frequency fO of the reflection coefficient frequency characteristic of the grating reflector, then Llfo≦fr≦2 The distance between the interdigital electrode and the grating reflector is set to be .0fr.

FIG. 2 is a diagram showing the frequency characteristics of the radiation conductance Gu of the interdigitated electrode 24 of the resonator shown in FIG. This is a reflection coefficient 1r'10 frequency characteristic. As can be seen from this figure, the peak of the radiation conductance is located at the high-frequency end of the reflection characteristic due to the above-mentioned configuration conditions. FIG. 3 shows the resonance characteristics of the resonator shown in FIG. In the figure, 3 is a resonance peak, and 4 is a longitudinal mode spurious. The resonance peak is on the higher frequency side compared to the resonance peak of the conventional device (FIG. 5).

In this example, the configuration conditions of the surface acoustic wave resonator are set so that the resonance peak 3 is located at the high-frequency end of the reflection characteristic 1, so the interval between the resonance peak 3 and the longitudinal mode spurious 4 is as follows. 5th @O Compared to the resonance characteristics of a conventional surface acoustic wave resonator, the resonance characteristics are wider than that of the New Year's Eve. Therefore, when used in a voltage controlled oscillator, it has the effect of widening the variable range of the oscillation frequency. Furthermore, there is also the effect that the vertical mode Sgelius 40 level is reduced.

〔Effect of the invention〕

As described above, according to the present invention, the effect of widening the interval between the resonance peak of the surface acoustic wave resonator and the longitudinal mode spurious is obtained, and when used in a voltage controlled oscillator, the frequency variable range can be widened.

[Brief explanation of the drawing]

1 is a plan view showing an embodiment of the present invention; FIG. 2 is a diagram showing the frequency characteristics of the radiation conductance of the interdigital electrodes of the surface acoustic wave resonator of FIG. 1 and the reflection coefficient of the grating reflector; Figure 3 is a diagram showing the resonance characteristics of the surface acoustic wave resonator shown in Figure 1, and Figure 4 is a diagram showing the radiation conductance of the interdigital electrodes and the frequency of the reflection coefficient of the crating reflector in a conventional surface acoustic wave resonator. Diagram Showing Characteristics The second revised diagram is a diagram showing resonance characteristics of a conventional surface acoustic wave resonator. Engineering: Radiation conductance, 2: Reflection characteristics, 3: Resonance peak, 4: Longitudinal mode spurious, 5°°°°° Radiation conductance , 6... Reflection percentage, 7... Resonance peak, 8... Longitudinal mode sgerious. Figure 5

Claims (1)

[Scope of Claims] In a surface acoustic wave resonator in which interdigitated metal film electrodes and a grating reflector are formed on a piezoelectric substrate, the mechanical impedance ratio of the surface acoustic wave of the metal film to the piezoelectric substrate is defined as Z= 1+ε (ε is the reflection ratio), and the ratio P/L of the period P of the grating reflector to the electrode period L of the interdigital electrode is ▲There are mathematical formulas, chemical formulas, tables, etc.▼, and the frequency at the resonance point is f_r is the center frequency fo of the reflection coefficient frequency characteristic of the grating reflector.
A surface acoustic wave resonator characterized in that a distance between the interdigital electrode and the grating reflector is set so that 1.1fo≦fr≦2.0fo.