JPS589603B2 - comb filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a comb-shaped filter having comb-shaped filter characteristics, and in particular, an attempt is made to eliminate cross-color interference appearing on the screen of a color television receiver by combining a reflective ultrasonic delay medium with an electromechanical transducer element. It is something to do.

Conventionally, this type of comb-shaped filter is configured so that ultrasonic waves pass through the interior of glass, which is a delay medium, and the overall shape is extremely large, requiring less installation space when used in a television receiver. There were many inconveniences.

In particular, recent television receivers employ integrated circuits and have extremely small internal chassis, so there is a demand for smaller receivers.

Therefore, the present invention aims to provide a small, high-performance comb-shaped filter.By utilizing surface waves, the thickness of the glass delay medium can be made extremely thin (less than several times the wavelength). It attempts to significantly reduce loss by configuring it in a reflective form, making it ultra-small, and by utilizing surface waves.

Currently, in the color television broadcasting system based on the NTSC system, 3. A carrier color signal obtained by modulating a 58 MHz color subcarrier with a color signal is interpolated and multiplexed within the high frequency band of the luminance signal as a color signal.

That is, as shown in Fig. 1, the high frequency components of the luminance signal indicated by the broken line are inserted into the color signal band indicated by the solid line in a frequency interleaved relationship, so the high frequency components of the luminance signal are This appears on the screen as cross-color interference, and this is considered to be a serious flaw in the NTSC system.

In order to eliminate this interference, it is clear that the color signal component should not include the high-frequency component of the luminance signal shown by the broken line in FIG. 1, and only the signal component shown by the solid line should be separated and extracted.

As means for separating this unnecessary signal, a comb-shaped filter whose maximum attenuation point is repeated at a period of the horizontal scanning frequency fH may be used, and such a filter can be realized using a delay circuit of 1/fH-Td.

FIG. 2 is a characteristic curve diagram of a comb filter used for the above purpose. In order to realize a comb filter with such characteristics, an input signal 1nwt and a signal sin (wt − wTd ) in opposite phases.

V(1-ωSwTd)2 in the above equation represents the amplitude characteristic of the comb filter shown in FIG.

The present applicant previously proposed a comb-shaped filter using a reflective ultrasonic delay medium as a delay element in patent application No. 71769/1983. The present invention provides a comb-shaped filter of this type, which utilizes surface waves to eliminate cross-color interference particularly in color television broadcasting, and which is constructed in an ultra-thin shape.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 3 shows a front view of the comb-shaped filter, and FIG. 4 shows a plan view thereof.

1 is a delay medium made of glass and has a hexagonal ultra-thin shape (
approximately 1 mm).

On both sides of the upper part of the delay medium 1, first and second end surfaces 2 and 3 are formed at an angle of 45 degrees with respect to the end surface direction of each end forming the outer peripheral surface of the delay medium 1. ing.

A transducer 4 having a thickness-traversing vibration mode is provided on the first end surface 2 via a common electrode 5, and an input electrode 6 and an output electrode 7 are provided on the transducer 4.
are provided, and an input terminal 8, an output terminal 9, and a common terminal 10 are respectively led out from these electrodes to constitute an electromechanical transducer T.

In this case, the input electrode 6 and the output electrode 7 are formed close to each other as shown in the figure, so that when an input electrical signal is applied between the input terminal 8 and the common terminal 10, there is no substantial delay from the input electrical signal. It is configured such that an output electrical signal is obtained between the output terminal 9 and the common terminal 10.

Further, absorption gates 11 made of epoxy resin are provided on the outer periphery of both sides of the delay medium 1 in order to prevent a part of the ultrasonic beam from reaching the transducer 4 on the output side without passing through the regular path. A total of six coats are provided, five along the sides and one in the center.

Figure 3 shows the delay medium 1 in order to reduce the overall shape.
are provided with reflective surfaces 12a, 12b, 12c, and 12d, the reflective surfaces 12a, 12b, and 12c form an angle of 45° with respect to the end surface portion 2 to which the electromechanical element T is attached, and the reflective surface 12d forms an angle of 45 degrees with respect to the end surface portion 2. The ultrasonic waves are formed so as to form an angle of 90 degrees, and the ultrasonic waves are reflected seven times, so that an electrical signal delayed with respect to an input electrical signal is superimposed with an opposite phase.

Here, the end face portion 2, the reflective surfaces 12a, 12b, 12c, and 12d are all formed at right angles to both surfaces of the delay medium 1, and the reflective surfaces 12a and 1'2c are parallel to each other, and the reflective surfaces 12b, 12c, and 12d are parallel to each other.
are formed at right angles to the reflective surfaces 12a and 12c.

In the above configuration, when an input electric signal is supplied between the input terminal 8 and the common terminal 10, this is applied between the electrodes 625 of the electromechanical transducer T, so the transducer 4 vibrates, and based on this, the input electric signal is applied between the electrodes 625 of the electromechanical transducer T. An output electrical signal that is not substantially delayed from the electrical signal is obtained between the electrodes 7 and 5, and this also extends the surface of the delay medium 1 from the end face 2 side to 12a, 12b, 12c, 12d as shown by the arrow in FIG. ,1
2c, 12b, and 12a, the ultrasonic wave is reflected seven times and directed toward the end face 2, and is applied to the transducer 4 of the electromechanical transducer T, so that the ultrasonic wave now reciprocates on the surface of the delay medium 1. Assuming that the time required for
An output electric signal derived without passing through the ultrasonic delay medium 1, that is, an output electric signal of the same phase with no substantial delay with respect to the input electric signal, and an output electric signal delayed by the time Td with respect to the input electric signal. A composite output electrical signal is obtained by combining the output electrical signals of opposite phases.

In this case, if the amplitude of the output electrical signal of the same phase is smaller than that of the delayed output electrical signal of the opposite phase, a coupling capacitor is inserted or formed between the input and output terminals 8 and 9 to reduce the voltage amplitude. reduction can be prevented.

To further explain the propagation of delayed ultrasonic waves, the ultrasonic beam traveling from the end face 2 spreads and propagates on the surface of the delay medium, but the ultrasonic waves indicated by the arrows are slightly deviated from the direction perpendicular to the end face 2 as described above. Reflective surface 12a, 1
It is reflected back by 2b, 12c, 12a and 12d and reaches the end surface 2 under the output electrode 7 via 12c, 12b, 12a, and an output electrical signal is obtained between the output electrodes 7 and 5 due to the vibration of the transducer 4. .

Also, although not shown, the ultrasonic waves traveling in a direction perpendicular to the end face portion 2 are incident on the reflecting surfaces 12a, 12b, and 12c at an angle of 45°, reflected at an angle of 45°, and incident on 12d at an angle of 90°. After reflection, the direction of the ultrasonic wave is changed by 180 degrees and takes the same path as the ultrasonic wave that reaches the reflecting surface 12d, and reaches the end surface portion 2 under the input electrode 7 via 12c, 12b, and 12a, and due to the vibration of the transducer 4, the output electrode 7, An output electrical signal is obtained during 5 minutes.

In this way, the ultrasonic waves traveling perpendicularly or in other directions from the end face part 2 are reflected an odd number of times by turning around the reflecting surface 12d on the way, and all those heading towards the end face part 2 are reflected between the output electrodes 7 and 5 due to the vibration of the transducer 4. Generates an output electrical signal.

Here, the propagation path between the absorption gates is between the absorption gate 11 in the center and the absorption gate 11 in the lower left corner of FIG. The reciprocating ultrasound waves pass together.

The delay medium 1 has a reflective surface 12 on which the ultrasonic wave is reflected an odd number of times.
a to 12d, and since the phase of the ultrasonic wave is reversed each time it is reflected, the delayed electrical signal sin (wt - wTd) is superimposed on the input electrical signal Sinwt with an opposite phase. , and its amplitude characteristic is υ7−(
1s-wTd)2, thus forming a comb-shaped filter with a response characteristic that is repeated in synchronization with one horizontal synchronization frequency fH as shown in FIG.

Therefore, the delay medium 1 may have any shape as long as the ultrasonic wave is reflected an odd number of times.

As described above, according to the present invention, one transducer having input and output electrodes formed close to each other on the upper surface is attached to an odd number of reflection type delay medium via a common electrode, and the transducer can be easily attached. This is extremely useful in practice because a comb-shaped filter for removing cross-color interference is constructed.

Further, since the reciprocating ultrasonic waves pass through the propagation path between the gates, it is suitable for miniaturization.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the spectral distribution of the luminance signal and color signal in NTSC color television broadcasting, where the solid line represents the color signal component and the broken line represents the luminance signal component, respectively. Figure 2 is a characteristic curve diagram of the comb filter. Third
The figure is a front view showing an example of the comb-shaped filter of the present invention, and FIG. 4 is a plan view thereof. In the figure, 1 is a delay medium, 4 is a transducer, 5 is a common electrode, 6 is an input electrode, 7 is an output electrode, and 11 is an absorption gate.

Claims (1)

[Claims] 1. A thin plate-shaped ultrasonic delay medium having a rectangular main surface with multiple corners cut out at an angle of 45°, and a plurality of gates for absorbing unnecessary waves provided at selected locations on the main surface; One transducer has input and output electrodes formed close to each other on the upper surface on one of the cutout surfaces, and an electromechanical transducer attached via a common electrode, and an input terminal connected to the input electrode is provided with an electromechanical transducer. reflecting the ultrasonic waves generated in the electromechanical transducer based on the input electrical signal on the reflective surface of the delay medium to be on the other side of the notch surface;
The ultrasonic wave reflected from the other notched surface is turned back and propagated in the opposite direction substantially parallel to the ultrasonic wave before reflection, and after being reflected on the reflecting surface of the delay medium an odd number of times, it is outputted via an electromechanical transducer. The transducer is configured to take out an output electrical signal to an output terminal connected to an electrode, and to allow the ultrasonic waves traveling in opposite directions to pass together through an ultrasonic path formed between the gates, and to operate the transducer based on the input electrical signal. The output terminal outputs a composite output electric signal obtained by combining the output electric signal derived directly via the input electric signal and the output electric signal delayed from the input electric signal by the time required for the ultrasonic wave to travel back and forth through the ultrasonic delay medium. Comb-shaped filter for better performance.