JPS5837727B2 - frequency selection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency selection device using surface acoustic waves.

Conventionally, (l) has been used as a frequency selection element in a frequency selection device for selecting a specific frequency component from a signal.
(2) A resonant circuit using electrical inductance (coil) and capacitance (capacitor), (2) A circuit using mechanical resonance (
mechanical filters), (3) those using piezoelectric bulk resonance (ceramic filters, crystal filters), (4
) Surface acoustic wave filters, resonators, etc. are known.

Among these, (1) has the advantage that the selection frequency can be varied over a wide range, but it is difficult to obtain a large selectivity Q due to the resistance component of the element, and The disadvantage is that the selected frequency is likely to change.

On the other hand, the items (2) to (4) have the advantage that it is relatively easy to increase the selectivity Q, but on the other hand, because they are essentially fixed frequency selection elements, the frequency range that can be varied is narrow. There was a drawback.

An object of the present invention is to provide a frequency selection device that can widen the variable frequency range and significantly increase the selectivity Q.

In order to achieve such an objective, the present invention provides at least one reflective electrode in close proximity to at least one surface acoustic wave transducer provided on the acoustic wave propagation line, and the reflective electrode is The feature is that frequency selection is performed by reflecting frequency components selected by parametric interaction with applied alternating current electrical signals.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of a frequency selection device according to the present invention.

In the figure, 1 is a signal input transducer, 2 is a signal output transducer, 3 and 4 are pump electrodes, 5 is a piezoelectric film, 6 is an insulating film, 7 is a semiconductor substrate, 8 and 9 are surface acoustic wave absorbers, and 10 is a pump 11 is a DC blocking capacitor, 12 is an AC blocking inductor, and 13 is a DC bias power source.

When manufacturing such a device, an insulating film 6 such as a silicon oxide film SiO2 is formed by thermal oxidation on a semiconductor substrate T made of silicon Si, etc., and a film such as zinc oxide ZnO or the like is deposited thereon by a sputtering method or the like. A piezoelectric film 5 is attached.

Furthermore, a gold layer such as aluminum A7 is evaporated on top of it,
Each electrode 1 to 4 is formed by photo-etching.

Electrodes 1 and 2 formed at the center of the surface of the piezoelectric film are comb-shaped electrodes, and constitute a signal input and signal output transducer.

Further, electrodes 3 and 4 formed in the vicinity of electrodes 1 and 2 are pump electrodes connected to a DC bias power supply 13 via an AC blocking inductor 12, and connected to a DC blocking capacitor 11. Pump power supply 1 through
Furthermore, surface acoustic wave absorbers 8 and 9 are arranged on both end faces of the sound wave propagation line of the piezoelectric film 5.

Note that the material of the piezoelectric film 5 is not limited to zinc oxide ZnO, but also lithium niobate LiN603, aluminum nitride A7N. Cadmium sulfide CdS. A piezoelectric material such as zinc sulfide Zn8 can be used, and as the semiconductor substrate 7,
Either P-type or N-type semiconductor may be used, and P-type or N-type semiconductor may be used.
The polarity of the voltage of the DC bias power supply 13 may be set to a polarity such that an appropriate space charge layer capacitance is generated on the surface of the semiconductor substrate 7 in accordance with each type.

Further, in the figure, an insulating film 6 as a stabilizing film is interposed between the semiconductor substrate 7 and the piezoelectric film 5, but depending on the material of the piezoelectric film, this insulating film 6 may be omitted.
It is also possible to use a piezoelectric substrate with a semiconductor film attached thereto.

In the configuration described above, a DC bias voltage is applied to the pump electrodes 3 and 4 by the DC bias power supply 13 so that an appropriate space charge layer capacitance is generated on the surface of the semiconductor substrate 7 directly under these electrodes 3 and 4. do.

Further, the output of the pump power supply 10 that generates a pump voltage with a frequency 2f that is twice the selected desired frequency f is applied to the pump electrodes 3 and 4 through the DC blocking capacitor 11, and the space charge layer capacitance on the surface of the semiconductor substrate 7 is increased by the pump voltage. frequency 2f of
Excite with

Since this capacitance changes depending on the applied voltage, it changes at a frequency of 2f.

On the other hand, when an input electrical signal is applied to the terminal 1' of the signal input transducer 1 having a sufficiently wide band, the input signal is converted into a surface acoustic wave signal and propagates on the surface of the piezoelectric film 5 to the left and right in the figure.

Among the surface acoustic waves propagating from the input transducer 1 to the left in the figure, the frequency f component is propagated through the pump electrode 3, and its piezoelectric potential increases the pump voltage due to the nonlinear effect of the space charge layer capacitance on the substrate surface. is amplified to perform parametric interaction with

At the same time, a surface acoustic wave with a frequency f corresponding to the magnitude of the input signal is generated, which propagates from the pump electrode 3 to the right in the figure.

This surface acoustic wave is propagated to the right in the figure and is again converted into an electrical signal by the signal output transducer 2, and a signal of the desired frequency f is output from its terminal 2'.

Similarly, among the surface acoustic waves propagated from the input transducer 1 to the right in the figure, a reflected wave with a frequency f corresponding to the magnitude of the signal of the frequency f component is propagated from the pump electrode 4 to the left in the figure. , is converted into an electrical signal by the output transducer 2.

That is, the surface acoustic waves reflected by the pump electrodes 3 and 4 are mainly components of frequency f, the magnitude of which corresponds to the input signal and also depends on the magnitudes of the pump voltage and bias voltage. .

Therefore, the frequency characteristic of the output of the output transducer 2 becomes as shown in FIG. 2a, and frequency selection with extremely high selectivity Q is possible.

Further, by changing the pump voltage frequency 2f of the pump power supply 10, the passband center frequency f extracted from the output transducer 2 can be varied.

Note that the passing surface acoustic waves propagated from the pump electrodes 3 and 4 to the left and right in the figure, respectively, are absorbed by the surface acoustic wave absorbers 8 and 9.

3 to 6 each show a schematic structure of another embodiment of the frequency selection device according to the present invention.

In the example of FIG. 3, one surface acoustic wave transducer 1
Reflective electrodes (pump electrodes) 3 and 4, which apply only the AC pump voltage of the pump power supply 10, are arranged close to both sides of the pump power source 10 to utilize changes in electrical impedance depending on the frequency of the transducer 14.

In the example of FIG. 4, a mechanically reflecting periodic concavo-convex member 20 is arranged on one side in the vicinity of input and output transducers 1 and 2 as surface acoustic wave transducers, and a pump on the other side. A reflective electrode 4 to which an AC voltage from a power source 10 is applied is provided.

In the embodiment shown in FIG. 5, two desired frequencies f1 and f2 are selected. Separate pump power supplies 15 and 16 are connected to the two pump electrodes 3 and 4, and the pump voltage of each pump power supply 15 and 16 is frequency to 2f1 and 2f
This is an example where the number is set to 2.

As a result, the frequency characteristic of the output taken out from the output transducer 2 becomes as shown in FIG. 2b.

In the embodiment shown in FIG. 6, the output to the output terminal 2' of the output transducer 2 is passed through a feedback circuit 17 to be fed back to the DC bias power supply 13 and the pump power supply 10, and the DC current is applied to the pump electrodes 3 and 4 as reflective electrodes. This is an example in which the amplitude and frequency of the output signal are controlled by changing the magnitude of the bias voltage and the magnitude and frequency of the AC voltage.

In this case, the feedback signal may be applied to either one of power supplies 13 and 10.

It goes without saying that the device shown in FIG. 6 described above can also be applied to the devices having the configurations shown in FIGS. 4 and 5.

Further, in the above-described embodiments, a case was described in which a reflective electrode having a uniform thickness is used, but the reflective electrode may have a periodic structure, for example, a comb-shaped structure.

Note that in that case, the frequency of the pump power source is not necessarily twice the selected desired frequency.

Further, in the above-described embodiment, the reflective electrode is provided outside the two elastic surface acoustic wave transducers, but it may also be provided between them.As described above, according to the present invention, The selected frequency range can be changed over a wide range simply by changing the frequency of the pump power supply.
Furthermore, the selectivity of the selected frequency can be significantly increased.

Furthermore, since the stability of the selected frequency can be determined by the stability of the external oscillator, it can be made extremely stable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an example of a frequency selection device according to the present invention, FIG. 2 is a characteristic diagram showing an example of frequency characteristics according to the present invention, and FIGS. 3 to 6 are respectively diagrams of a frequency selection device according to the present invention. FIG. 2 is a schematic horizontal diagram of another embodiment of the invention. 1 is a signal transducer, 2 is a signal output transducer, 3 and 4 are pump electrodes, 5 is a piezoelectric film 10 which is a pump power source, and 13 is a DC bias power source.

Claims (1)

[Scope of Claims] 1. Signal input and signal output surface acoustic wave transducers are arranged on a sound wave propagation line formed on a piezoelectric element, and on the sound wave propagation line other than between both surface acoustic wave transducers, A frequency selection device characterized in that reflective electrodes are arranged and means for applying a DC signal and an AC signal to the reflective electrodes is provided. 2. According to claim 1, at least one of a DC signal and an AC signal applied to the reflective electrode is controlled by a feedback signal of the output of the signal output surface acoustic wave transducer. frequency selection device.