JPS61191189A - Comb line filter - Google Patents

Abstract

PURPOSE:To improve separation rate characteristic by using two delay circuits that delay input signals only for 1 horizontal period, two arithmetic circuits that make addition and subtraction, and an attenuating circuit that attenuates by specified gain. CONSTITUTION:The first and second delay circuit 5, 6 that delay input signals from an input terminal by 1 horizontal period respectively and an attenuating circuit 7 that attenuates input signals by a fixed gain K are used. Output signals of the delay circuit 6 and output signals of the attenuating circuit 7 are added by the first arithmetic circuit 8, and output signals of the arithmetic circuit 8 and output signals of the delay circuit 5 are processed by the second arithmetic circuit 9. When luminance signals are taken out from the arithmetic circuit 9 to an output terminal 4, gain of frequency characteristic 2 of a comb line filter becomes close to zero in the wide range near the trough point, and accordingly, carrier chrominance signals do not leak to the terminal 4.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a comb filter suitable for use in video equipment such as color television receivers and video tape recorders.

In a color video signal, the luminance signal and carrier chrominance signal are transmitted by frequency interleaving, so on the receiving side, the luminance signal and carrier chrominance signal must be separated and extracted from the color video signal. However, there is a comb filter as a filter for this separation.

<Prior Art> Fig. 2 shows an example of a comb filter commonly used in the past. In this example, it is a C-shaped comb filter for extracting a luminance signal from a color video signal, and I is a color video signal. A signal input terminal, 2 a delay circuit whose delay time is one horizontal period TD, 3 an adder circuit, and 4 an output terminal for a luminance signal.

If the levels of the input signal and output signal (-luminance signal) are Ei and Eo, respectively, and the angular frequency of the input signal is ω (=2πf), then the frequency characteristic (frequency vs. amplitude) of the comb filter shown in Fig. 2 is characteristics) are expressed by the following equation.

=12th place--]-1 Therefore, if the frequency characteristics of this comb filter are illustrated,
The curve will look like the curve ■ in Figure 3, where n is a positive integer and fH (-I/TD) is the horizontal frequency, when f = nfH.
When AVI=2,=2n+I,H AV! =0. The luminance signal and the carrier color signal are each
・Since it has frequency components as shown in Figures A and BK,・
A luminance signal is taken out to terminal 4.

<Problem to be solved by the invention> However, in this comb filter system, the valley point (f=2 fH
), AVl=O, and if the frequency deviates even slightly from the valley point, the gain AVI will suddenly increase, so
The carrier color signal shown in FIG. This will be reproduced as cross color, reducing the image quality.

Means for Solving the Problems> The present invention has been made in view of the above points, and includes two delay circuits, a first and a second delay circuit, each of which delays an input signal by one horizontal period (1H); A comb-shaped filter with excellent separation characteristics is created by using two arithmetic circuits, first and second, which perform addition and subtraction processing on two input signals, respectively, and a subtraction circuit that attenuates the input signal with a predetermined gain. It is composed of

<Example> The embodiments shown in the drawings will be described below.

FIG. 1 shows a system diagram of one embodiment of the comb filter of the present invention, in which input signals including a luminance signal and a carrier color signal supplied from a 5-Fi input terminal l are input for one horizontal period (1H).
The first delay circuit 6 delays the input signal by 1
7 is an attenuation circuit that attenuates the input signal by a constant gain K (however, K(+)); 8 is an output signal of the second delay circuit 6 and an output signal of the attenuation circuit 7; 9 is a second arithmetic circuit that subtracts the output signal of the first arithmetic circuit 8 and the output signal of the first delay circuit 5; Only the luminance signal is separated and derived from the second arithmetic circuit 9 to the output terminal 4.

The frequency characteristics of the comb filter configured as described above are expressed by the following equation.

ωTD ωTD IAV2+ = 12cO3 1+4cos2] Therefore, if the frequency characteristics of this comb filter are illustrated, it will look like the curve ■ in Figure 4, and when 2n+1 f ”S 薯fu (trough point), AV2=02n+
1 n f When n < f < 薯璽 fH (near the valley point), V2
-PK When f=nfH (top of the mountain), AV2=+2. .

Therefore, compared to the characteristic curve (2) Fi characteristic curve (2), the gain AV2 is small in a wide range near the valley point and close to 0, so that the carrier color signal does not leak to the output terminal 4.

<Effects of the Invention> Thus, according to the present invention, it is possible to obtain characteristics with excellent separation as a comb filter, and it is possible to faithfully separate and extract only the luminance signal component.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of one embodiment of the comb filter of the present invention,
Fig. 2 is a system diagram of conventional comb filters, Fig. 3 is a diagram showing the characteristics of these comb filters, and Fig. 4 is a frequency spectrum diagram of an input signal to explain the operation of the comb filter of the present invention. It is. 1...Input terminal, 4...Output terminal, 5...
...First delay circuit, 6...Second delay circuit, 7
...attenuation circuit, 8...first arithmetic circuit, 9
...Second arithmetic circuit. Agent Patent Attorney Aihiko Fuku (and 2 others) Stimulating comb-shaped filter thread 81m Figure 2 2! ! −j−1fHnf, 2n, +l ,, f
%jI wavenumber characteristic diagram of KuLsugiηruta Figure 3 River wave list τ7 ratio diagram of input signal

Claims (1)

[Claims] 1. A first delay circuit to which an input signal including a luminance signal and a carrier color signal is supplied and delayed by one horizontal period (1H), and a signal delayed by 1H in the first delay circuit is further delayed by 1H. a second delay circuit, an attenuation circuit to which the input signal is supplied and attenuated with a predetermined gain, an output signal of the second delay circuit and an output signal of the attenuation circuit are supplied, and both signals are subjected to addition processing. a first arithmetic circuit that is supplied with an output signal of the first arithmetic circuit and an output signal of the first delay circuit, and a second arithmetic circuit that performs subtraction processing on both signals; A comb filter characterized in that a luminance signal is obtained as an output signal of an arithmetic circuit.