JPH02108308A - Surface acoustic wave oscillator - Google Patents

Abstract

PURPOSE:To improve frequency stability with respect to the fluctuation of a load by providing output side IDTs at prescribed intervals on both sides of an input side IDT on a piezoelectric substrate electrically connecting them in parallel, and further, providing an output fetching IDT on the same propagating path. CONSTITUTION:A surface acoustic wave delay line 20 has an input side IDT 22, output side IDTs 23 and 24 arranged on both sides of the IDT 22, and an output fetching IDT arranged on the same propagating path as that of the IDTs 22 to 24 on a piezoelectric substrate 21. An interval L1 between the input side IDT 22 and the output side IDT 23 is determined by an expression I, and an interval L2 between the input side IDT 22 and the output side IDT 24 is determined by an expression II. In the expressions I and II, (m) and (n) mean integers, and lambda0 means the wavelength of the surface acoustic wave corresponding to the central frequencies of the respective IDTs. The output side IDTs 23 and 24 are electrically connected in parallel to each other. An input side port 26 and an output side port 27 are connected to a phase shifter and an amplifier, which are connected into a loop, constitute a surface acoustic wave oscillator, and the oscillating output is fetched from an output fetching port 28.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave oscillator using a surface acoustic wave delay line.

[Conventional technology]

Conventional examples of this type of surface acoustic wave oscillator are shown in Figures 3 and 4.
Each is shown in the figure.

All surface acoustic wave oscillators basically consist of an amplifier 2, a phase shifter 4 for phase adjustment that satisfies oscillation conditions, and a two-boat surface acoustic wave delay line 10 connected in a loop. It is configured. However, the phase shifter 4 may be inserted on the input side of the amplifier 20 in some cases. Further, impedance matching circuits 6 and 8 are usually inserted on the input/output side of the surface acoustic wave delay line 10 as in this example, but this is not essential.

In the example shown in Figure 3, a directional coupler (
Alternatively, a circulator (circulator) 12 is used to suppress interference from subsequent stages.

On the other hand, in the example shown in FIG. 4, the output is simply taken out using a capacitor 14 instead of the directional coupler 12 as described above. However, in this case, there is no effect of preventing interference from subsequent stages, and therefore, in order to prevent fluctuations in the oscillation frequency due to load fluctuations, it is necessary to take measures such as providing a buffer amplifier 16 at the next stage.

[Problem to be solved by the invention]

As mentioned above, in conventional surface acoustic wave oscillators, in order to prevent interference from subsequent stages, a directional coupler 12 is used as in the example shown in Figure 3, or a buffer amplifier is used as in the example in Figure 4. Measures have been taken to insert 16.
The former is expensive because it uses a special component called the directional coupler 12, and the latter also uses a buffer amplifier 16, which makes it expensive and requires space for it.

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface acoustic wave oscillator that can suppress interference from subsequent stages without using a directional coupler, buffer amplifier, or the like as described above.

[Means for Solving the Problems] In order to achieve the above object, the surface acoustic wave oscillator of the present invention includes at least one input side IDT on one piezoelectric substrate as a surface acoustic wave delay line as described above. , ((1/4)+m}λ0 and ((1
/4)+n}λ0 (where m, , n are integers, λ. is each I
at least two output-side IDTs spaced apart from each other by a wavelength of surface acoustic waves corresponding to the center frequency of the DTs and electrically connected in parallel to each other;
It is characterized in that it has an IDT for output extraction arranged on the same propagation path as the DT.

[Effect]

In the above-mentioned surface acoustic wave delay line, the surface acoustic waves excited at the input side IDT are converted into in-phase electrical signals at the output side IDTs on both sides due to the above-mentioned phase relationship, and are outputted while reinforcing each other. be done. On the other hand, the surface acoustic wave that has passed through any of the output side IDTs is converted into an electrical signal by the output extraction IDT, and this becomes the output of the surface acoustic wave oscillator.

On the other hand, if part of the output returns to this output take-out IDT due to load fluctuations in the next stage or later, part of the surface acoustic waves re-excited in this IDT will be transferred to the output side. The signals are converted into electrical signals by each output IDT and then combined toward the IDT, but since there is a 180 degree phase difference between the output IDTs, these electrical signals weaken each other. . Therefore, by such an effect, interference from the next stage and subsequent stages can be suppressed.

〔Example〕

FIG. 1 is a block diagram showing a surface acoustic wave oscillator according to an embodiment of the present invention, and FIG. 2 is a diagram showing an example of the configuration of a surface acoustic wave delay line in FIG. 1. Figures 3 and 4
Portions equivalent to those in the illustrated example are given the same reference numerals, and differences from the conventional example will be mainly explained below.

In the surface acoustic wave oscillator of this embodiment, a surface acoustic wave delay line 20 having a structure as shown in FIG. 2 is used in place of the conventional surface acoustic wave delay line 10.

This surface acoustic wave delay line 20 includes, on one piezoelectric substrate 21, one input side IDT 22, two output side IDTs 23 and 24 arranged on both sides of this input side IDT 22, and the same IDTs 22 to 24. It has an output extraction IDT 25 arranged on the propagation path.

The distance L+ between the input side IDT 22 and the output side IDT 23 is L+ = ((1/4)+m}λ0... (1),
Also, the distance L2 between the input side IDT 22 and the output side IDT 24
is Lx = ((1/4)+n) λ. ... Each of (2) has been selected. Here, m and n are integers and λ. is the wavelength of the surface acoustic wave with respect to the center frequency f0 of each IDT 22 to 24, and ■=λ. f, (v is the propagation velocity of the surface acoustic wave).

The re-output side IDTs 23 and 24 are electrically parallel to each other and connected to an output side port 27, and this output side port 27 is connected to the amplifier 2 via an impedance matching circuit 8 as shown in FIG. is connected to the input section of the

In addition, the input side IDT 22 is connected to an input side port 26, and this input side port 26 is connected to the output section of the amplifier 2 via an impedance matching circuit 6 and a phase shifter 4, as shown in FIG. has been done.

In addition, the output takeout IDT25 is the output takeout port 2.
8, from which the oscillation output is extracted.

In the surface acoustic wave delay line 20, the input side IDT 2
When an electrical signal is applied to 2, surface acoustic waves 31.
32 are excited, and the surface acoustic waves 31, 32 reach the output IDTs 23, 24, where they are converted into electrical signals. In that case, there is a gap between the output side IDT 23 and the output side IDT 24 seen from the input side IDT 22 as described in (1) above.
As can be seen from equation (2), there is no phase difference, so the electrical signal converted by the output side IDT 23 and the output side IDT 24
The converted electrical signals are outputted to the output side boat 27 while reinforcing each other.

Also, if we focus on the surface acoustic wave 32 side, a part of it passes through the output side IDT 24 without being converted into an electrical signal, but the surface acoustic wave 33 that has passed through this output side IDT 24 reaches the output extraction IDT 25. There, it is converted into an electrical signal and output to the output extraction boat 28. This becomes the output of the surface acoustic wave oscillator. By the way, the amount converted into an electrical signal by this output IDT 25 is about 1/4 when viewed from the input side IDT 22, and the amount converted to an electrical signal by the output side IDT 22
It becomes 1/2 when viewed from 24.

On the other hand, if we consider the case where an impedance mismatch occurs due to load fluctuations in the next stage or later, and a part of the output returns to this rDT 25 for output extraction, The electrical signal is re-excited into a surface acoustic wave, and a part of the surface acoustic wave 34 is transmitted to the output side ID.
Head towards T24 etc. And this surface acoustic wave 34 is
It reaches the output side IDT 24, where it is converted into an electrical signal,
In addition, the surface acoustic wave 35 that has passed there is also transferred to the output side IDT 23.
, where it is converted into an electrical signal, and both electrical signals are combined and output to the output port 27.

However, between the output side IDTs 23 and 24, the above (
As can be seen from equations 1) and (2), 180 degrees (i.e. λ./
2) Because of the phase difference, the electrical signal output from the output side DT 23 and the electrical signal output from the output side IDT 24 will weaken each other, and therefore the electrical signal returned to the output extraction IDT 25 The degree to which is outputted from the output side port 27 becomes very small. In other words, a so-called acoustic directional coupler is formed in this surface acoustic wave delay line 20, and due to this action,
Interference from subsequent stages can be suppressed.

Strictly speaking, the surface acoustic waves 35 that reach the output side IDT 23 are smaller than the surface acoustic waves 34 that reach the output side IDT 24, so there is a difference in the amplitude of the electrical signals output from these waves, and they do not cancel each other out completely. However, compared to the case where the phase difference is not considered at all, the canceling effect by adding a phase difference of 180 degrees as described above is sufficient.

Therefore, by using the surface acoustic wave delay line 20 as described above, interference from the next stage and subsequent stages can be suppressed without using the expensive directional coupler 12, buffer amplifier 16, etc. as in the conventional example. . That is, the frequency stability of the surface acoustic wave oscillator against load fluctuations can be improved.

Although the surface acoustic wave delay line 20 with one input side IDT has been described above, a plurality of input side IDTs may be arranged in parallel and electrically connected to each other in parallel, and each input side IDT may be connected in parallel with each other.
Output side IDTs are arranged on both sides of the DT while maintaining the same relationship as in equations (1) and (2) above, and each output side IDT is arranged on both sides of the DT.
The DTs may be electrically connected in parallel with each other, and in this case, the effect similar to the above-mentioned directional coupler can be performed more effectively.

〔Effect of the invention〕

As described above, according to the present invention, a so-called acoustic directional coupler is formed in the surface acoustic wave delay line. Interference from subsequent stages can be suppressed. That is, the frequency stability of the surface acoustic wave oscillator against load fluctuations can be improved. Furthermore, the cost is lower than when using a directional coupler, a buffer amplifier, etc., and the space can also be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a surface acoustic wave oscillator according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of the structure of the surface acoustic wave delay line in FIG. 1. FIGS. 3 and 4 are block diagrams showing examples of conventional surface acoustic wave oscillators, respectively. 2... Amplifier, 4... Phase shifter, 20... Surface acoustic wave delay line, 21... Piezoelectric substrate, 22... Input end ID
T, 23.24... Output side IDT, 25... IDT for output extraction.

Claims (1)

[Claims] (1) In a surface acoustic wave oscillator configured by connecting an amplifier, a phase shifter, and a surface acoustic wave delay line in a loop, at least one input is provided on one piezoelectric substrate as the surface acoustic wave delay line. side IDT and on both sides of each input side IDT {
(1/4)+m}λ_0 and {(1/4)+n}λ_
At least two output-side IDTs spaced apart by 0 (where m and n are integers, and λ_0 is the wavelength of the surface acoustic wave corresponding to the center frequency of each IDT) and electrically connected in parallel to each other. 1. A surface acoustic wave oscillator characterized in that the surface acoustic wave oscillator further comprises: and an output extraction IDT disposed on the same propagation path as these IDTs.