JPS5847089B2 - Color television receiver PIF surface wave filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color television receiver PIF surface wave filter.

It is well known that PIF filters for color television receivers are formed using surface acoustic wave devices.

It is also well known that this PIF filter is an asymmetric filter having a predetermined level audio carrier trap (8 points) and an adjacent channel video carrier trap (Q point) as shown in FIG.

When this filter is formed by a surface acoustic wave device, it is generally constructed as shown in FIG.

That is, weighting is performed manually or by weighting the output electrode so as to meet the specifications of the PIF filter.For example, as shown in FIG. The surface acoustic wave 4 from the transducer 3 is provided with an output electrode 5 at a predetermined distance of 2° to obtain a filter characteristic.

However, when a filter configured in this manner is used as a PIF filter for a color television receiver, surface waves are transmitted directly between the input terminal of the input electrode 2 and the output terminal of the output electrode 5 without passing through the surface waves. This has the disadvantage that it interferes with signals transmitted through the passband, resulting in ripples or spurs in the passband.

Such spurious causes the disadvantage of bostra occurring in the image of a color television receiver.As a means to improve this spurious, the distance between the manual electrode 2 and the output electrode 5 is set at 2° to approximately 40 times the wavelength at the center frequency. It is also known that if the length is increased to a certain extent, spurious components can be improved and desired PIF filter characteristics can be obtained.

However, in this case, if the distance 2° is made 40 times the wavelength, the maximum active aperture length (WLM) of the human-powered electrode 2 is ff
It is necessary to set it to i200λ0.

(λ0...Surface wave wavelength of center frequency) Therefore, not only the size of the filter becomes large, but also the input/output impedance is extremely small, and matching with the circuits before and after the PIF filter of a color television receiver is required. There is a drawback that cannot be removed.

If the distance is further increased by 2 degrees, the propagating surface waves will cause a diffraction phenomenon, and the attenuation amount of the attenuation pole of the filter characteristics will deteriorate.

According to our calculations and experiments for TV PIF filters, we found that due to diffraction, the attenuation at the 8 points increases compared to when diffraction can be ignored, and at the Q point, the attenuation decreases compared to when diffraction can be ignored. Ta.

It is known that as a means to improve the reduction in the amount of attenuation in the trap, by increasing the length of the output electrode, the output electrode approaches the design value while vibrating.

However, like the PIF filter of a color television receiver, there are two trap levels, namely the audio trap (8
There was no guarantee that it would be possible to obtain an asymmetric filter in which the video carrier (point Q) and the video carrier of the adjacent channel (point Q) had to be set at different predetermined levels.

The present invention has been made in view of the above points, and includes audio traps of a predetermined level (8 points) and video carriers of adjacent channels (Q).
Asymmetric color television receiver PIF with
A surface skin filter is provided.

That is, the human-powered electrode is composed of an apodized interdigital interdigital electrode, the output electrode is composed of an interdigital transducer with a constant active aperture length, and the aperture length of the output electrode is 1.05 times the maximum flame of the active aperture length of the input electrode. This invention provides a PIF surface wave filter for a color television receiver set to a trap level 'tJ constant of 1.70 times.

Next, embodiments of the filter of the present invention will be described with reference to the drawings.

An apodized interdigital interdigital electrode 22 and an interdigital output electrode 23 having a constant opening length are provided on a piezoelectric material such as a ceramic substrate 21.

The input electrode 24 has a PIF filter characteristic by changing the cross axis, that is, has an apodized structure.

The aperture length (RM) of the output electrode 24 is 1.05 to 1.7 times the active aperture length maximum flame (WLM) of the input electrode 22.
Form to 0x.

Sound-absorbing material 24.2 is provided in the passage of the input/output electrodes 22.23.
5 is provided.

The distance stone between this waiting force electrode 22 and output electrode 23 is 2oλ
FIG. 4 shows the relationship between the maximum directivity (WLM) of the active aperture length of the human electrode and the aperture length ratio M of the "optimal" human/output electrode when the angles are set to 0°, 4oλo, and 7oλ0°.

The meaning of this "optimal" will be explained later.

The change in filter characteristics when changing the aperture length ratio is shown in Part 5.
As shown in the figure.

It is calculated as zo-40λ0.

In Fig. 5, S in a color television receiver is
The setting position of point Q is 17 at 54.25MHz for 8 points.
．． Range of 5db to 20db, R point is 60.2M
It is necessary to keep it below 40db at Hz, and in FIG. 5, the distance (zo) between the person and the output electrodes 22 and 23 is 40λ.

Here, the aperture length ratio M (-) when the aperture length (WLM) of the human electrode 22 is 33λ0 is taken as a parameter.

WLM According to FIG. 5, it can be seen that when the aperture length ratio is set to 1.3, both the 8 points and the Q point satisfy the PIF filter conditions.

This filter characteristic curve gradually changes, and Figure 5 shows that in the 1.2 direction and 1.4 direction of the aperture at the Q point and the length ratio of 1.3, there are many values that satisfy the Q point condition. I'm having a meal.

Figure 4 mentioned earlier shows the distance between the person and the output electrodes 22 and 23 (
Optimal human-powered electrode 2 that satisfies the conditions for the S point and Q point of the PIF filter when zo) is 20λo, 40λo, and 70λ0
This shows the change when the maximum aperture length of No. 2 is changed, and shows that the optimum [direction] changes depending on the aperture length of the human-powered electrode.

Figure 6 shows the characteristics when 2°=70λ0.

In this way, it was found that the aperture length ratio of the S point and Q point of the PIF filter satisfies the above conditions in the range of 1.05 to 1.7.As explained above, according to the present invention, the PIF filter It is possible to obtain a surface wave filter that satisfies the characteristics of

Furthermore, it has the effect of reducing spurious noise more than conventional skin filters.

In the above embodiment, an example in which ceramic is used as the piezoelectric material has been described, but any piezoelectric material such as LiNbO3 or quartz may be used.

Furthermore, using a LiTaO3 plate with good surface wave propagation efficiency as a substrate, LiNbO3 with good electricity-to-surface wave conversion efficiency is formed only for forming the human output electrode, and the human output electrode is formed on this LiNbOa piezoelectric material. Good too.

When using a material with a large coupling coefficient, as shown in Figure 3, if the lead wire extraction electrode is brought close to the active electrode, the diffracted surface wave will receive all of the phase distortion at this electrode, as shown in Figure 7. Although the effects of the present invention may be hindered, in such a case, as shown in FIG. 8, it can be achieved by sufficiently separating the leads so as not to disturb the propagation path of the surface waves of the electrode for leading out the lead wires.

[Brief Description of the Drawings] Fig. 1 is a PIF filter characteristic curve diagram of a well-known color TV receiver, Fig. 2 is a conventional surface wave filter for obtaining the characteristics shown in Fig. 1, and Fig. 3 is a filter of the present invention. FIG. 4 is a diagram showing the change in the optimum alignment when changing 2 degrees in FIG. 3, and FIG. 5 is a diagram showing the change in the optimum alignment when 2 degrees in FIG. Figure 6 is a filter characteristic diagram when 2° = 70λ of Figure 4
. FIG. 7 is an explanatory diagram of factors that inhibit the effect of the present invention when the coupling coefficient is large, and FIG. 8 is a filter characteristic diagram when the coupling coefficient is large.
It is another practical explanatory view of the figure. In the figure, 21... piezoelectric body, 22...
・Manual electrode, 23... Output electrode, 24/25
°゛°゛°°Absorber・(WLM)...Manual electrode aperture length, (RM)...Output electrode aperture length.

Claims (1)

[Claims] 1. An apodized interdigital input electrode for exciting a surface acoustic wave provided on a piezoelectric material, and an apodized interdigital input electrode for exciting a surface acoustic wave provided on the piezoelectric material in a surface acoustic wave propagation path from the electrode. It comprises a comb-like output electrode for converting into an electrical signal, and means for making the active aperture length of the output electrode 1.05 times to 1.70 times the maximum length of the active aperture length of the input electrode. A color television receiver PIF surface wave filter characterized by: 2. A PIF surface wave filter for a color television receiver according to claim 1, wherein the apodized interdigital input electrode is a weighted PIF filter. 3. A color television receiver PIF surface wave receiver according to claim 1, wherein the piezoelectric body is a ceramic.