JP2531020B2 - Surface acoustic wave oscillator - Google Patents

Description

TECHNICAL FIELD 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 FIGS. 3 and 4, respectively.

Basically, any surface acoustic wave oscillator has an amplifier 2
And a phase shifter 4 for phase adjustment that satisfies the oscillation condition, and 2
A port-type surface acoustic wave delay line 10 is connected in a loop shape. However, the phase shifter 4 may be inserted in the input side of the amplifier 2. Further, impedance matching circuits 6 and 8 are usually inserted on the input and output sides of the surface acoustic wave delay line 10 as in this example, but they are not essential.

In the example shown in FIG. 3, the directional coupler (or circulator) 12 is used for taking out the output to suppress the interference from the subsequent stages.

On the other hand, in the example of FIG. 4, the output is taken out simply by using the capacitor 14 instead of the directional coupler 12 as described above. However, in this case, there is no effect of preventing interference from the next stage onward, so in order to prevent fluctuations in the oscillation frequency due to load fluctuations, the buffer amplifier 16
You must take measures such as setting up.

[Problems to be Solved by the Invention]

As described above, in the conventional surface acoustic wave oscillator, the directional coupler 12 is used as in the example of FIG. 3 or the buffer amplifier is used as in the example of FIG. 4 in order to prevent interference from the subsequent stages. Although a means for inserting 16 is taken, the former is expensive because it uses a special component called the directional coupler 12, and the latter is also expensive because it uses the buffer amplifier 16, and the space for it is also large. There is a problem that it becomes necessary.

Therefore, an object of the present invention is to provide a surface acoustic wave oscillator capable of suppressing interference from the next stage onward without using the directional coupler or the buffer amplifier as described above.

[Means for solving the problem]

In order to achieve the above object, the surface acoustic wave oscillator of the present invention, as the surface acoustic wave delay line as described above, at least one input side IDT on one piezoelectric substrate, and each input side IT.
{(1/4) + m} λ ₀ and {(1/4) + n} on both sides of DT
λ ₀ (where m and n are integers, λ ₀ is the wavelength of the elastic surface corresponding to the center frequency of each IDT), and at least two output-side IDTs are electrically connected in parallel. And an IDT for output extraction arranged on the same propagation path as these IDTs.

[Action]

In the surface acoustic wave delay line, the surface acoustic waves excited by the input-side IDT are converted into electrical signals in phase with each other by the output-side IDTs on both sides of the surface acoustic wave, and are mutually strengthened and output. To be done. Also, output IDT on one side
The surface acoustic wave that has passed through is converted into an electric signal by the output extraction IDT, and this becomes the output of the surface acoustic wave oscillator.

On the other hand, when a part of the output returns to this output extraction IDT due to load fluctuation after the next stage, a part of the surface acoustic wave re-excited by this IDT will be The output side IDTs convert and combine the electric signals toward the IDTs and the like. However, since there is a phase difference of 180 degrees between the output side IDTs, the electric signals weaken each other. Therefore, by such an action, it is possible to suppress the interference from the next stage onward.

〔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 a configuration of a surface acoustic wave delay line in FIG. The same parts as those in the example of FIGS. 3 and 4 are designated by the same reference numerals, and the differences from the conventional example will be mainly described 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 as an alternative to the conventional surface acoustic wave delay line 10.

This surface acoustic wave delay line 20 is on one pressure transmission substrate 21,
One input side IDT22, two output side IDTs 23 and 24 arranged on both sides of this input side IDT22, and these IDTs 22 to 24
And an output take-out IDT 25 arranged on the same propagation path.

The distance L ₁ between the input-side IDT 22 and the output-side IDT 23 is L ₁ = {(1/4) + m} λ ₀ (1), and the distance L ₂ between the input-side IDT 22 and the output-side IDT 24 is L ₂ = {(1/4) + n} λ ₀ (2). Here, m and n are integers, λ ₀ is the wavelength of the surface acoustic wave with respect to the center frequency f ₀ of each IDT 22-24, and there is a relationship of v = λ ₀ f ₀ (v is the propagation velocity of the surface acoustic wave).

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

The input side IDT 22 is connected to the input side port 26, and the input side port 26 is connected to the output section of the amplifier 2 via the impedance matching circuit 6 and the phase shifter 4 as shown in FIG. ing.

Further, the output take-out IDT 25 is connected to the output take-out port 28, through which the oscillation output is taken out.

In the surface acoustic wave delay line 20, when an electric signal is applied to the input side IDT 22, the surface acoustic waves 31 and 32 are excited, and the surface acoustic waves 31 and 32 are respectively output side IDT2.
It reaches 3, 24, where it is converted to an electrical signal. In that case, there is no phase difference between the output-side IDT23 and the output-side IDT24 viewed from the input-side IDT22, as can be seen from the above equations (1) and (2). The electric signal and the electric signal converted by the output side IDT 24 are mutually strengthened and output to the output side port 27.

Also, focusing on the surface acoustic wave 32 side, part of it is on the output side.
Although the IDT24 passes through it without being converted into an electric signal, the surface acoustic wave 33 that has passed through this output side IDT24 is output I
It reaches DT25, where it is converted into an electric signal and output to the output extraction port 28. Then, this becomes the output of the surface acoustic wave oscillator. By the way, this output IDT25
The amount converted into an electric signal by the input IDT22 is about 1
/ 4, 1/2 when viewed from the output side IDT24.

On the other hand, consider a case where an impedance mismatch occurs due to load fluctuations in the subsequent stages, etc., and part of the output returns to this output extraction IDT25.
The electric signal returned at the IDT 25 is re-excited into a surface acoustic wave, and a part of the surface acoustic wave 34 goes toward the output side IDT 24 and the like. The surface acoustic wave 34 reaches the output side IDT 24 and is converted into an electric signal there, and the surface acoustic wave 35 passing therethrough also reaches the output side IDT 23 and is converted into an electric signal there, and both electric signals are combined. And is output to the output side port 27.

However, between the output side IDTs 23 and 24, as can be seen from the above equations (1) and (2), 180 degrees (that is, λ ₀ /
Because of the phase difference of 2), the electric signal output from the output side IDT23 and the electric signal output from the output side IDT24 weaken each other, so that the electric signal returned to the output extraction IDT25 is The degree of output from the output port 27 is extremely small. That is, this surface acoustic wave delay line 20
In other words, it means that an acoustic directional coupler is formed, and by such an action, it is possible to suppress the interference from the subsequent stages.

Strictly speaking, the surface acoustic wave 3 reaching the output IDT 23
Since 5 is less than the surface acoustic wave 34 reaching the output side IDT, there is a difference in the amplitude of the electric signals output from these, and they are not completely offset, but compared to the case where no phase difference is considered, There is a sufficient effect of cancellation by adding a phase difference of 180 degrees as shown in.

Therefore, by using the surface acoustic wave delay line 20 as described above, it is possible to suppress interference from the next stage onward without using the expensive directional coupler 12, buffer amplifier 16 or the like as in the conventional example. . That is, the frequency stability of the surface acoustic wave oscillator with respect to load fluctuation can be improved.

In the above, the input side IDT exemplifies one surface acoustic wave delay line 20, but a plurality of input side IDTs are arranged in parallel and electrically connected in parallel with each other, and the above-mentioned is provided on both sides of each input side IDT. The output side IDTs may be respectively arranged while maintaining the same relations as in the equations (1) and (2), and the output side IDTs may be electrically connected in parallel to each other. The action like a directional coupler can be more effectively performed.

〔The invention's effect〕

As described above, according to the present invention, the electric signal applied to the input-side IDT is converted into a surface acoustic wave there, and the electric signals of the same phase are respectively output at the output-side IDTs arranged on both sides of the input-side IDT. The electric signals returned from the outside to the IDT for output extraction are converted into surface acoustic waves at the IDT for output and then output to the IDT on the input side.
Output side IDTs located on both sides of the output side convert each to an electrical signal with a phase difference of 180 degrees and weaken each other for output, so there is no need to use a directional coupler or buffer amplifier, etc. Can be suppressed. As a result, it is possible to improve the frequency stability of the surface acoustic wave oscillator of the present invention with respect to load fluctuations. In addition, the cost is lower and the space can be reduced as compared with the case of using a directional coupler, a buffer amplifier, or the like.

[Brief description 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. 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 side IDT, 23,24 …… Output side IDT, 25 …… Output output IDT .

Claims (1)

(57) [Claims] 1. A surface acoustic wave oscillator configured by connecting an amplifier, a phase shifter, and a surface acoustic wave delay line in a loop shape, wherein at least one surface acoustic wave delay line is formed on one piezoelectric substrate. One input-side IDT and {(1/4) + m} λ ₀ and {(1/4) + n} λ ₀ on each side of each input-side IDT (where m and n are integers, λ ₀ is the center of each IDT). At least two output-side IDTs that are placed apart from each other by the wavelength of the surface acoustic wave corresponding to the frequency and are electrically connected in parallel with each other, and output extractions that are placed on the same propagation path as these IDTs A surface acoustic wave oscillator, characterized in that one having an IDT for use is used.