JPS5828935B2 - Dansei Hiyoumenhasouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave device suitable for being incorporated in a receiver for receiving a modulated carrier signal, particularly in an FM and PM receiver.

FM and PM receivers adopt a single or double superheterodyne reception method, and their standard configuration is to first amplify the received input signal from the antenna with a high-frequency circuit, and then mix this with the first local oscillator and output. into a circuit and converted to a first intermediate wave number.

In the case of the double superheterodyne reception method, the second
The signal is converted to an intermediate frequency and then sent to an amplifier and demodulator.

Currently, crystal oscillators are used as local oscillators, but
This utilizes the stable mechanical natural vibration of a quartz plate through its piezoelectricity, and thickness shear vibration is usually used.

Since the resonant frequency is inversely proportional to the plate thickness, the higher the frequency, the thinner the plate must be, and when using the fundamental mode, the upper limit is about 25 MHz.

Therefore, if it is desired to obtain a stable oscillator in a frequency band higher than this, it is necessary to perform overtone excitation such as 3rd order or 5th order, or to use a multiplier.

Furthermore, these outputs contain frequency components other than the desired order, and if these are led directly to the mixer, problems such as spurious radiation will occur. Therefore, a filter that passes only the desired frequency components is installed before the mixer. must be inserted.

On the other hand, a surface acoustic wave oscillator that combines a surface acoustic wave delay line and an amplifier can easily oscillate in the fundamental mode up to around IGHz.
Filters etc. are not required.

Furthermore, after the received carrier signal is amplified by a high frequency circuit, a front end filter is inserted to suppress the image frequency relative to the first intermediate frequency.

This filter and the above-mentioned unnecessary order suppression filter are usually L
Because it is made of C, the other circuits that make up the receiver are I.
Compared to carbon, which is becoming increasingly popular, it occupies a relatively large volume and is one of the obstacles to miniaturization.

Therefore, it would be a great advantage if the front-end filter and oscillator could be realized on a single substrate by applying surface acoustic waves.

An object of the present invention is to provide a new surface acoustic wave device in which the local oscillator and front-end filter are monolithically constructed.

According to the present invention, the amplifier and the first converter provided on the piezoelectric substrate convert an electrical signal into a surface acoustic wave signal or vice versa.
and a second interdigital transducer, a third interdigital transducer formed on the same substrate and converting the modulated carrier wave signal into a surface acoustic wave, and an elastic transducer from the first interdigital transducer. a synchronous grating that allows the surface waves to pass through and reflects the surface acoustic waves from the third interdigital transducer to guide both surface acoustic waves in the same direction; and a fourth synchronous grating that converts both surface acoustic wave signals into electrical signals. A surface acoustic wave device consisting of interdigital transducers is obtained.

Therefore, if the fourth interdigital transducer is connected to a frequency mixing circuit, a signal converted to an intermediate frequency is obtained at the output of the mixing circuit.

Next, the present invention will be explained with reference to the drawings.

The figure shows an embodiment of a surface acoustic wave device according to the present invention.

In the figure, reference numeral 1 denotes a piezoelectric substrate, the whole surface of which is mirror polished, and interdigital transducers 2 and 3 are placed facing each other on this substrate.

Furthermore, these transducers are connected to the input terminals of the amplifier.
When a suitable electrical signal is applied, the amplified electrical output is converted into a surface acoustic wave by the interdigital transducer 2,
The wave propagates along the surface of the substrate 1 in the direction of the arrow 5 and is delayed by the interdigital transducer 3, where the surface acoustic wave is converted back into an electric signal by a piezoelectric reaction.

This electrical signal becomes the input to the amplifier 4 again.

Therefore, the amplification degree of the amplifier 4 is equal to that of the transducer 2°3.
An oscillator can be realized by selecting amplitude conditions that are more favorable than losses due to propagation and conversion of surface acoustic waves in a delay line constructed of .

The oscillation frequency is determined by φ, which is the phase lag in the delay line, and φ, which is the phase lag in the electrical circuit including the amplifier.

Then, it is a frequency that satisfies .

In a surface acoustic wave delay line, n is usually a value of several tens to several hundreds, so it is possible to oscillate at a very large number of frequencies, but by making the number of electrode pairs of the interdigital transducer sufficiently large, it is possible to oscillate at only one frequency. The amplitude condition can be satisfied,
A stable oscillator can be obtained.

Since the interdigital transducer 2 is bidirectional, the surface acoustic waves propagate not only in the direction of the arrow 5 but also in the direction of the arrow 6, and do not substantially affect the periodic grating 7 disposed on the propagation path. The light passes through without being affected and is converted into an electrical signal by the interdigital transducer 8.

On the other hand, the interdigital transducer 9 is arranged so that the surface acoustic wave excited from this transducer propagates in a direction perpendicular to the surface acoustic wave from the oscillator and reaches the periodic grating.

Now, when an electrical signal with a frequency f8 is applied to the interdigital transducer 9, a surface acoustic wave with the same frequency is excited and propagates in the direction of the arrow 10, but is reflected by the periodic grating 7 and is reflected by the arrow 10.
The signal propagates in one direction and is converted into an electrical signal by a converter 8.

The periodic grating 7 is formed by forming periodic conductor strips on the piezoelectric substrate 1 or by providing periodic grooves.

If the period of the grating is 1, the wave vector has IKI
=2π/l.

The wave number vectors of the incident wave and reflected wave are given separately.

Assuming that a gold-incident surface acoustic wave is reflected by a periodic grating tilted at an angle θ with respect to its propagation direction and propagates in a perpendicular direction, the following must be satisfied.

In this 5, νin, ν. 1 is the sound velocity of the surface acoustic wave entering and exiting the periodic grating, and since the substrate 1 is an anisotropic body, generally ν.

Note that ut are not equal.

Further, f8 is the frequency of the input signal.

Therefore, if the angle θ and the period ■ are set so as to satisfy the above equations (2) and (3) for the surface acoustic wave (frequency f ) from the interdigital transducer 9, the periodic grating can be used as a good reflector. Become.

On the other hand, the elastic surface from the oscillator has the frequency f of the carrier signal.
Since the frequency is different from 8, it does not satisfy equation (3) among the reflection conditions, and therefore it simply passes through the periodic grating.

Since the output of the interdigital transducer 8 contains the frequency component of the local oscillator and the received input signal, it is converted to an intermediate frequency by introducing it into a mixing circuit.

Since the surface acoustic wave oscillator keeps the loop gain constant due to the saturation characteristics of the amplifier, it contains a considerable amount of harmonic components, especially second harmonic components, due to its nonlinearity.

However, in this embodiment, these harmonic components are sufficiently suppressed by passing through the interdigital transducers 2 and 8.

This is because, as an example, a transducer that responds efficiently at a certain frequency will not respond at a frequency twice that frequency.

In addition, the characteristics as a front-end filter are realized by the interdigital transducer 9, the periodic grating 7, and the interdigital transducer 8, and it is desirable to design each pattern so that sufficient attenuation is obtained especially at the image frequency relative to the intermediate frequency. .

As explained above, in the present invention, although the oscillator and the front-end filter are formed on the same substrate and have a single output terminal, the oscillator operates stably because they do not interfere with each other.

In the embodiment described above, the interdigital transducer 9 is arranged perpendicularly to the other interdigital transducers, but the arrangement as shown in the figure may not be possible depending on the directional dependence of the piezoelectricity of the substrate material. It may happen.

In this case, the interdigital transducer 9 is placed parallel to the other transducers, and the surface acoustic waves excited by the transducer 9 are reflected by a newly provided periodic grating and then incident on the periodic grating 7. That's fine.

[Brief explanation of the drawing]

The figure shows an embodiment of a surface acoustic wave device according to the present invention, 1
is a piezoelectric substrate; 2, 3, 8, and 9 are interdigital transducers; 7 is a periodic grating that reflects or transmits surface acoustic waves; and 4 is an amplifier.

Claims (1)

[Claims] 1. An oscillator comprising an amplifier and a first interdigital transducer provided on a piezoelectric substrate that converts an electric signal into a surface acoustic wave signal, and a second interdigital transducer that converts the surface acoustic wave signal into an electric signal; a third interdigital transducer formed on the same piezoelectric substrate and converting a modulated electrical input signal into a surface acoustic wave signal; and a surface acoustic wave signal excited by the first interdigital transducer are allowed to pass through; It is comprised of a periodic grating that guides both surface acoustic waves in the same direction by reflecting the modulated surface acoustic waves, and a fourth interdigital transducer that converts both of the surface acoustic wave signals into electrical signals. A surface acoustic wave device characterized by: