JPS6353515A - Transducer array for surface acoustic wave - Google Patents

Abstract

PURPOSE:To obtain uniform surface acoustic wave intensity over a wide frequency range with low power consumption, by individually providing amplifiers to be used for driving transducers. CONSTITUTION:High-frequency signals produced by a variable frequency oscillator 11 are distributed by a distributing circuit 16 and inputted to transducers (IDT) 3-6 through variable phase shifters 14 and amplifiers 17-20, respectively. Since each IDT has its own center frequency and natural frequency band width, only one or two IDTs are driven and caused to produce surface acoustic waves (SAW). When the resistance of the electrode finger of each IDT is reduced and, at the same time, the impedance inside the natural frequency band is matched to a signal source side, high-frequency signals are reflected from the IDTs 3, 5, and 6, whose input high-frequency signals are outside the natural frequency bands, and respectively returned to the amplifiers 17, 19, and 20. Since the reflected high-frequency signals hardly returns to the distributor 16 through the variable phase shifters 14, appearance of ripples is eliminated and characteristic deterioration hardly takes place.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a leading wave acousto-optic
.

Surface acoustic wave (Su
rface acoustic wave, hereinafter SA
The present invention relates to transducer arrays (referred to as W), and in particular to surface acoustic wave transducer arrays with improved drive circuits.

[Prior Art] Broadband transducers are increasingly required to be used as components of optical waveguide type AO equipment such as optical deflectors, spectrum analyzers, and correlators. Several methods are already known for making broadband SAW transducers. A plurality of comb-shaped transducers (with different center frequencies)
A multi-working tilted 11 SAW transducer array (MT
The advantage of the S array is that it has a simple structure and that electrical adjustment after fabrication of the transducer is done in a circuit.

Such an MTS array excites surface acoustic waves in an optical waveguide, and creates a desired AO between the guided light propagating in the optical waveguide.
In order to produce the effect, it is necessary to apply a high frequency signal with a specific frequency and power to each T. Such high frequency signals are generally generated and amplified by an electrical circuit before being input to the IDT. These electric circuits are called IDT drive circuits.

FIG. 3 is a schematic diagram showing an example of a configuration of a conventional surface acoustic wave transducer array that also includes a T drive circuit.

In FIG. 3, 1 is a leading waveguide made of 〒i diffused LiNh03, etc., 2 is guided light (incident light) propagating through the optical waveguide, and 3, 4, and 5.6 have different center frequencies, respectively. In addition, the IDTs are arranged at different inclination angles with respect to the guided light 2, 7 is a SAW that is excited from the IDT and propagates through the optical waveguide 1, and 8 is a SAW generated when the incident light 2 is diffracted by the SAW. It is diffracted light,
9 is undiffracted light.

The high frequency signal generated by the variable frequency oscillator 11 is amplified to a desired power by an amplifier 12, and then distributed by a power divider 13, and then distributed by a variable phase shifter 14.
and is input to the IDTs 3, 4, 5.6 via the matching circuit 15. Since each IDT has a different center frequency and natural frequency bandwidth, effectively only one or at most two of the four IDTs are driven to generate a SAW. FIG. 3 depicts the case where the drive frequency of the transducer array is such that the SAW is excited only from IDT 4. I
The 5AW7 excited by the DT4 acts as a diffraction grating that moves with respect to the incident light 2, and a part of the incident light 2 undergoes Bragg diffraction and becomes the diffracted light 8, and a part passes through as is and becomes the undiffracted light 9. The diffracted light 8 is separated from the undiffracted light 9 and used for signal processing, recording, etc.

In addition, the variable phase shifter 14 compensates for the phase difference between the diffracted lights by each IDT at the crossover frequency of two adjacent strands T, and adjusts the phase of each SAW so that the SAWs from the two IDTs strengthen each other. This is to adjust the By appropriately setting the arrangement of each IDT, the same effect can be obtained by omitting the variable phase shifter as described above (see Japanese Patent Laid-Open No. 117527/1983).

[Problem to be solved by the invention 1 In the above-described transducer array,
In order to reduce the power consumption of the drive circuit, it is sufficient to reduce the insertion loss of the variable phase shifter and matching circuit, and
Regarding T, it is sufficient to reduce the electrode finger resistance and match the impedance within the specific pass frequency band with the signal source side.

However, if the electrode finger resistance in the IDT is reduced and the impedance within the pass frequency band is matched with the signal source side, the IDT
becomes a high impedance, and the high frequency signal input to the IDT is reflected back to the signal source side with almost no loss. The reflected signal passes through the matching circuit 5 and the variable phase shifter 14, but since passive reciprocal circuits are generally used as these electric circuits, when the insertion loss of these circuits is reduced as described above, The reflected high frequency signal from the IDT side passes through with almost no steep loss and returns to the power divider 13 again, and is then connected to the amplifier 1.
2 to the distributor 13.

For example, as shown in FIG.
If the high frequency signal from T is a signal near the center frequency of IDT 4, the high frequency signal is outside the frequency band of IDT 3.5.6, so the high frequency signal reflected from T is sent to power divider 13. Return, from the amplifier 12 to the distributor 1
Since the phase of the high-frequency signal that is reflected by each IDT and returns to the power divider 13, which interferes with the input signal to IDT 3, differs depending on the frequency, the frequency characteristics of the high-frequency signal that interferes with these and input to IDT 4 has severe ripples. occurs.

FIG. 4 is a graph showing the simulation results of ripple occurrence as described above. In this simulation, there are three IDTs making up the transducer, each IDT has five pairs of electrode fingers, and the center frequency is 360 MHz for the first IDT and 400 MHz for the second IDT.
MHz, the third IDT is 440MHz, and each IDT
are respectively matched to a signal source of 50Ω using inductors, and the same effect can be obtained by omitting the use of a variable phase shifter by appropriately setting the IDT arrangement.

In FIG. 4, #1, #2, #3 are respectively the fifteenth second . The dashed line indicates the third IDT.
The solid line shows the results when three IDTs were driven in parallel in the same manner as shown in FIG. 3 above. From FIG. It can be seen that due to the drive circuit configuration, significant ripples occur within the frequency band due to reflected high frequency signals from other IDTs.

When such ripples occur in the frequency characteristics of the high-frequency signal input to the IDT, the intensity of the SAW for diffracting the guided light 2 shown in FIG. 3 changes depending on the frequency, and as a result, the intensity of the diffracted light 8 changes. It will vary depending on the frequency. Therefore, in a conventional transducer array as shown in Fig. 3, if you try to reduce the loss of each circuit part and reduce power consumption, it is difficult to respond to changes in the frequency of the high-frequency signal used to excite the 5AW7. Therefore, there was a problem that the intensity of the diffracted light 8 could not be made uniform.

Therefore, the present invention solves the problems in the conventional surface acoustic wave transducer array as described above, and provides a surface acoustic wave transformer that can obtain a similar surface acoustic wave intensity in a wide frequency range with low power consumption. The purpose of the present invention is to provide a deuser array.

[Means for Solving the Problems] According to the present invention, in order to achieve the above objects, in a surface acoustic wave transducer array comprising a plurality of surface acoustic wave transducers, A surface acoustic wave transducer array is provided, characterized in that an amplifier is individually provided for driving each transducer.

[Example] Hereinafter, specific examples of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing a first embodiment of a surface acoustic wave transducer array according to the present invention.

In FIG. 1, l is a leading waveguide made of diffused LiNbO3, etc., 2 is a guided light (incident light) propagating through the optical waveguide, and 3, 4, and 5.6 each have a different center frequency. In addition, the IDTs are arranged at different inclination angles with respect to the guided light 2, 7 is a SAW that is excited from the IDT and propagates through the optical waveguide 1, and 8 is the diffraction generated when the incident light 2 is diffracted by the SAW. is light,
9 is undiffracted light. 17.18, 19.20 is IDT
It is an amplifier for driving, and includes the variable phase shifter 14 and each IDT.
It is interposed between.

The high frequency signal generated by the variable frequency oscillator 11 is distributed by a distribution circuit 16 and input to the IDTs 3 to 6 via the variable phase shifter 14 and the amplifiers 17 to 20, respectively. Since each IDT has a different center frequency and natural frequency band width, only one or at most two of the four IDTs are driven;
Generate SAW. Figure 1 is similar to Figure 3 above,
The drive frequency of the transducer array is SAW I
The case where the frequency is such that it is excited only from DT4 is depicted. 5AW7 excited by IDT4
acts as a diffraction grating that moves with respect to the incident light 2, a part of the incident light 2 undergoes Bragg diffraction and becomes diffracted light 8, and a part passes through as is and becomes undiffracted light 9. 0 Diffracted light 8 is undiffracted It is separated from the light 9 and used for signal processing, recording, etc.

In this embodiment as described above, when the electrode finger resistance of each EDT is reduced and the impedance within the natural frequency band is matched with the signal source side, the input Takaoka wave signal is outside the natural frequency band of the IDTs 3, 5, . 6, the high frequency signals are reflected back to amplifiers 17, 19 and 20, respectively. However, in general, increase If! When a signal is input from the output side, the ratio of the signal transmitted to the input side of the G-device, that is, the isolation, can be easily set to about -20 dB.

Therefore, the high frequency signals reflected from the IDTs 3, 5.6 hardly pass through the variable phase shifter 14 and return to the distributor 16, so that the high frequency signals reflected from the IDTs 3, 5. The appearance of ripples like the solid line in the graph of frequency characteristics disappears, thus almost no characteristic deterioration occurs.

FIG. 2 is a schematic diagram showing a second embodiment of the surface acoustic wave transducer array according to the present invention. In FIG. 2, the same components as in FIG. 1 are given the same reference numerals.

In FIG. 2, reference numerals 21, 22, 23, and 24 indicate frequency band filters, which are interposed between the distribution circuit 16 and each variable phase shifter 14. Each of these frequency band filters passes a high frequency signal having a band that is the same as or slightly wider than the natural pass frequency band of the IDTs 3, 4, and 5.6, and does not allow other signals to pass. When such a frequency band filter is used, if a signal in the non-pass band is input, there is a risk that the signal will be reflected in the filter, but it is necessary to allow a slight increase in insertion loss in the pass frequency band. For example, when a signal with a frequency in the non-pass band is incident, it is possible to substantially prevent the signal from being reflected from the filter to the input side, and in this embodiment, such a filter is used. use

Furthermore, amplifiers 25, 26, 27, and 28 are interposed between each variable phase shifter 14 and each IDT 3 to 6, respectively.

Preferably, the amplifier performs class B or class 0 amplification operation.

In this embodiment as described above, the variable frequency oscillator 11
The high frequency signal generated in the filter passes through the band filter and is input to the amplifier only when the frequency of the signal is within the pass frequency band of the frequency band filter.

The #14112 amplifier, which performs class B or class 0 operation, does not flow bias current, so its power consumption is extremely small when there is no signal.In addition, the 89115 amplifier or class C amplifier generally does not add harmonic components to the input signal. However, as mentioned above, the IDT uses the natural frequency lii! Since there is a range of 1, harmonic components are not converted to SAW, and there is virtually no problem in operation.

In this way, in this embodiment, all the amplifiers related to the IDT having a natural frequency band to which the frequency of the driving high-frequency signal does not belong are in a non-operating state, so that power consumption can be reduced compared to the first embodiment. It is a fair canter.

In the first and second embodiments described above, the SA from two twists T at the crossover frequency is achieved using a variable phase shifter.
However, in the present invention, without using such a variable phase shifter,
Similar effects can also be achieved by appropriately setting the arrangement of each IDT as described in Japanese Patent No. 17527.

In this case, in the first embodiment, the amount of phase shift of the amplifiers 17 to 20 is taken into consideration, and in the second embodiment, the amount of phase shift of the frequency band filters 21 to 24 and the amplifiers 25 to 28 is taken into consideration. Then, the arrangement may be determined so that the diffracted lights are strengthened at the crossover frequency of each IDT.

Furthermore, although the above embodiment shows a transducer array with four IDTs, in the present invention
Of course, the number of T's is not limited to four, and the present invention can be similarly applied to any transducer array having a plurality of IDTs.

Further, although FIG. 1 shows an example in which the variable phase shifter is provided between the distribution circuit and the amplifier, the variable phase shifter may also be provided between the amplifier and the IDT. Similarly, in FIG. 2, a variable phase shifter can be provided between the distribution circuit and the filter or between the amplifier and the IDT.

In addition, although FIGS. 1 and 2 above show a configuration in which the IDT and the amplifier are directly connected, if the output impedance of the amplifier and the input impedance of the IDT are different, the configuration shown in FIG. 3 above may be used. It is also possible to insert a matching circuit to reduce the irregular gold phase.

[Effects of the Invention] According to the present invention as described above, even when a high frequency signal with a frequency outside the natural frequency band of an IDT is input to the IDT, the reflected signal from the IDT is not the same as the input high frequency signal to another IDT. Because it is absorbed by the amplifier without interference,
It is possible to suppress the appearance of ripples in the frequency characteristics of the SAW excited from the IDT, and thus it is possible to obtain a surface acoustic wave transducer array in which the SAW intensity is similar over a wide frequency range with low power consumption.

[Brief explanation of the drawing]

1 and 2 are schematic configuration diagrams showing a surface acoustic wave transducer array according to the present invention. FIG. 3 is a schematic diagram showing an example of a conventional surface acoustic wave transducer array. FIG. 4 is a graph showing simulation results of ripple occurrence in a surface acoustic wave transducer array. 1: Guide wavepath, 2 Two-way radiation, 3-6: IDT, 7: SAW, 8: Diffracted light, 9: Non-diffracted light, 17-20.2
5-28: Amplifier. 21-24: Filter. Agent Patent Attorney Jo Taira Yamashita Figure 2 Figure 3 Figure ■ Wave number (MHX)

Claims (6)

[Claims] (1) A surface acoustic wave transducer array comprising a plurality of surface acoustic wave transducers, characterized in that an amplifier for driving each transducer is individually provided. Array. (2) The surface acoustic wave transducer array according to claim 1, wherein a high frequency signal emitted from a single variable frequency oscillator and distributed by a distribution means is inputted to each transducer via each amplifier. (3) The surface acoustic wave transducer array according to claim 1, which has a variable phase shifter before or after each amplifier. (4) The surface acoustic wave transducer array according to claim 1, wherein each high frequency signal is inputted to an amplifier via a frequency band filter. (5) The surface acoustic wave transducer array according to claim 1, wherein the amplifier is a class B amplifier or a class C amplifier. (6) The surface acoustic wave transducer array according to claim 1, wherein impedance matching means is interposed between each transducer and its driving means.