JPH0335851B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to surface acoustic wave devices, and particularly to improvements in comb-shaped surface acoustic wave devices used in video circuits of television receivers.

A comb filter is used in the video circuit of a large color television receiver. This comb-shaped filter is used for the purpose of reducing cross-color damage prevention and dot interference, and widening the video signal band.It consists of a delay line for one horizontal scanning period (hereinafter referred to as 1HDL). ing.

FIG. 1 shows the configuration of a video delay line according to the prior art. That is, in the conventional delay line, an ultrasonic transducer that performs electrical/acoustic conversion, consisting of a piezoelectric material 3 and input electrodes 1 and 1', is brought into close contact with the end face of a glass 4 as a propagation medium for ultrasonic signals. A piezoelectric material 3', an output electrode 2,
The output side vibrator, which performs acoustic/electrical conversion, is closely attached to the transducer 2'. Then, ultrasonic waves are emitted from the input-side transducer into the glass 4, and the glass 4
After the inside is reflected multiple times, an electrical signal is obtained from the vibrator on the output side.

FIG. 2 is a diagram showing the configuration of a known comb-shaped surface acoustic wave device. In this figure, a transmission-side interdigital electrode 8 and reception-side interdigital electrodes 7 and 9 are provided on a piezoelectric material 6, and AC power is applied to the transmission-side interdigital electrode 8 via a resistor 10. . Further, the interdigital electrodes 7 and 9 on the receiving side are connected in parallel, and a load resistor 11 is connected in parallel to these electrodes 7 and 9.

In such a configuration, when an electric signal is applied to the interdigital electrode 8 on the transmitting side, the electric signal is converted into an ultrasonic signal by the interdigital electrode 8. This ultrasonic signal propagates on the piezoelectric material 6 in the left-right direction,
It is received by interdigital electrodes 7 and 9. The amplitude frequency characteristics at this time are obtained by using the product of the propagation characteristics of the interdigitated electrode 8 on the transmitting side and the propagation characteristics of the interdigitated electrodes 7 and 9 on the receiving side as an envelope, and superimposing the difference in delay time to the two receiving electrodes on the envelope. It has the following characteristics.

However, in the conventional delay line described above, spurious responses occur unless the directivity of the elastic waves (SAW and bulk waves) propagating on a solid is made unidirectional. For this purpose, the width of the excitation electrode must necessarily be greater than a predetermined width.

In addition, since bulk waves are generally about 60% faster than surface waves, in order to obtain a predetermined delay time (1H), the size of the wave becomes large, and the device must also be made larger.

In general, conventional comb filters use the video signal of a television receiver as the frequency of the ultrasonic signal, and therefore have the disadvantage that it is difficult to miniaturize the surface acoustic wave device and it becomes expensive.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a surface acoustic wave device that eliminates the above-mentioned drawbacks of the prior art and is smaller in size and lower in price.

Therefore, the present invention integrates an IF filter and 1HDL, which is conventionally used in the video frequency band.
By using 1HDL in the IF frequency band, the delay line itself can be made smaller and the number of components can be reduced. That is, the present invention provides a first interdigital electrode that converts an electrical signal into a surface acoustic wave, a member that propagates the surface acoustic wave, and a member that converts the surface acoustic wave propagated through this member into an electrical signal. It has a second interdigital electrode, a third interdigital electrode, and these three
The propagation characteristics of the two interdigital electrodes are all different. Specifically, the difference between the delay time between the first interdigital electrode and the second interdigital electrode and the delay time between the first interdigital electrode and the third interdigital electrode is calculated as 1 of the television signal. This is set to the horizontal scanning time or a predetermined multiple thereof.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, the surface acoustic wave device is used in an IF circuit of a television receiver.

Referring to FIG. 3, the input interdigital electrode 1
An electrical signal is applied to 5, and this electrical signal is converted into a surface acoustic wave. Interdigital electrode 15 for input
The surface acoustic waves from the piezoelectric member 18 propagate on the piezoelectric member 18.
This piezoelectric material 18 is composed of, for example, a lithium niobate single crystal.

The surface acoustic waves propagated on the piezoelectric member 18 are received by the output interdigital electrodes 16 and 17, where the surface acoustic waves are converted into electrical signals. In this embodiment, the input and output interdigital electrodes 15, 1
6 and 17 are, for example, 5000 Å thick aluminum vapor-deposited films formed by photolithography.

The characteristic feature of this embodiment is the setting of the propagation characteristics of each interdigital electrode.

That is, the electrode width of the input interdigital electrode 15 is set to 8.6 μm and the logarithmic width is set so that the product of the propagation characteristics of the interdigital electrodes 15 and 16 becomes the characteristic 12 of the IF filter as shown in FIG. 4, a. is a normal-form double electrode structure with 15 pairs, and the output interdigital electrode 16 has a weighted double electrode structure with 50 pairs of electrode width and electrode spacing, and the distance between their centers is It was set to 4mm.

On the other hand, the product of the propagation characteristics of the interdigital electrodes 15 and 17 is 55.17MHz±0.5MHz, as shown in FIG.
In order to achieve characteristic 13 with a passband of cm. In this case, a reflective portion is also included as shown in the figure.

Therefore, since the output interdigital electrodes 16 and 17 are connected in parallel, a propagation characteristic 14 as shown in FIG. 4c is obtained as an output characteristic. In other words, it has a comb-shaped characteristic only between 55.17MHz±0.5MHz, and the comb interval is approximately 63.5μs for one horizontal scan.
(approximately 15.7 KHz), and has the characteristics of a conventional IF filter for television signals of other frequencies.

In this way, according to this embodiment, it is possible to integrate a conventional IF filter and a video delay line (1HDL), and the delay line in the video frequency band is formed in the IF band, making the device significantly smaller. can be converted into

Incidentally, the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications. For example, although a single sheet of piezoelectric material is used in the above embodiment, a piezoelectric thin film may be used only in the interdigital electrode portion, and glass may be used as the other propagation medium.

As explained above, according to the present invention, the IF filter and 1HDL are integrated, and the 1HDL conventionally used in the video frequency band is used in the IF frequency band. It is possible to reduce the price.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a video delay line according to the prior art, FIG. 2 is a diagram showing the configuration of a known comb-shaped surface acoustic wave device, and FIG. 3 is a diagram showing the configuration of a surface acoustic wave device according to an embodiment of the present invention. Figure 4 shows a, b,
c is a diagram showing frequency characteristics caused by the combination of each electrode shown in FIG. 3; Reference numeral 15 denotes an input interdigital electrode, 16 and 17 an output interdigital electrode, and 18 a piezoelectric member.

Claims (1)

[Claims] 1 A first interdigital electrode that converts an electric signal into a surface acoustic wave, and a second and third interdigital electrode that converts the surface acoustic wave into an electric signal are provided on the same piezoelectric substrate, The product of the propagation characteristics of the interdigital interdigital electrode and the second interdigital electrode has the characteristics of a video intermediate frequency filter of a color television receiver, and the product between the first interdigital interdigital electrode and the second interdigital electrode A surface acoustic wave device characterized in that the difference between the delay time and the delay time between the first interdigital electrode and the third interdigital electrode is set to one horizontal scanning time of a television signal or a predetermined multiple thereof.