JPS61242175A - Comb-line filter - Google Patents

Abstract

PURPOSE:To eliminate the need for signal capacity normalization circuits and to vary easily the coefficients of a coefficient multiplier by obtaining a circulating delay signal input from the output of the coefficient multiplier. CONSTITUTION:If the signal of a video signal input terminal 1 is Vi; the input signal of the coefficient multiplier 5 is V1; the output signal of its coefficient multiplier 5 is V2; the output of a signal output terminal 9 is V0; the feedback coefficient of the coefficient multiplier 5 is K; the transfer function of 1H delay circuit 3 is G, two equations are established as follows; V0=V1-V2=(1-K)V1, V1=Vi+GV2=Vi+KGV1. If V1 is eliminated from the above equation, the relation of the equation 1 is established between an input and output. Equation 2 shows a comb-line filter which has a venter at the integer magnification portion of a horizontal frequency. At this time, the signal level of the venter is 1 irrespective of the value of K.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a comb filter, and in particular, the present invention relates to a comb filter.
The present invention relates to the configuration of a circulating comb filter used for /N improvement, etc.

(1)
is a video signal input terminal, (2) is an arithmetic circuit, and (3) is a horizontal time delay circuit (hereinafter referred to as a horizontal time delay circuit).

(rlH delay circuit), (4) is an adder circuit.

(5) is a multiplier, (6) is a signal output terminal, and (7) is a signal amount normalization circuit.

Next, the S/N improvement operation in FIG. 2 will be explained. Now, the signal of the video signal input terminal (1) is connected to Vi, IH.
input signal of delay circuit (3) to vh, signal output terminal (6)
Let the signal of
If the transfer function of delay circuit g (3) is G, then the following equation holds true.

V h x Vi + K Vo...■
Vo-Vi+GVh =・@ ■, ■ When vh is deleted from the equation, the output signal V is obtained.

The relationship between the input signal Vl and the input signal Vl is expressed by the formula (2).

And IHil! ! The transfer function G of the spreading circuit (3) is τh-1/f when dealing with a television signal with a large line correlation.
h (fh is the line frequency).

It is expressed as G=e""=cos ωτh −Js+n ωτb. Therefore, the transfer function of equation (2) can be expressed as equation (2).

...■ If n is a positive integer, then the formula is f m n * fh
The reason for this is that the filter in Figure 2 is a comb-shaped filter that has a belly at an integer multiple of the horizontal frequency, and changing the feedback rate K changes the sharpness of the amplitude-frequency characteristic of the filter, so the S/N ratio increases. This indicates that the degree of improvement can be set freely.

Further, since the output signal of the signal amount normalization circuit (7) is a function of K, the signal is multiplied by (1-K) to prevent output convergence changes from occurring due to changes in K.

[Problems to be Solved by the Invention] In the conventional circuit described above, when the system aK of the multiplier (5) is changed in order to change the S/N improvement degree, the signal amount normalization circuit (7) changes. The multiplier must also be changed in proportion to K, making it difficult to obtain consistency between both circuits, and it has been difficult to substantially vary K.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a comb filter circuit that can easily change the coefficient of the coefficient.

[Means for Solving the Problems] The comb filter according to the present invention eliminates the need for a signal amount normalization circuit by obtaining the cyclically delayed signal input from the output of the multiplier.

[Operation] This invention eliminates the need for a signal amount normalization circuit, so by changing only the coefficient of the coefficient generator, the desired S/
N improvement degree can be easily obtained without any change in signal amount.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, the same symbols as in FIG. 2 indicate the same parts,
(1) is a video signal input terminal, (2) is an arithmetic circuit, (3)
is an IH1i extension circuit, i5) is a multiplier, (8) is a subtraction circuit, and (S) is a signal output terminal.

The video signal input terminal (1) is connected to one input of the arithmetic circuit (2), and the output of the arithmetic circuit (2) is input to the multiplier (5) and also serves as the subtracted input terminal of the subtraction circuit (8). is also entered. The output of the multiplier (5) is input to the subtraction input terminal of the subtraction circuit (8), and is also input to the subtraction input terminal of the subtraction circuit (8).
). Further, the output of the IH delay circuit (3) is connected to the other input of the arithmetic circuit (2). Further, the output of the subtraction circuit (8) is connected to a signal output terminal (9). Note that the arithmetic circuit (2) is composed of an adder circuit that adds two inputs.

Next, the operation will be explained. In Figure 1, the signal of the video signal input terminal (1) is Vi, the input signal of the multiplier (5) is Vl, the output signal of the multiplier (5) is V2, and the output of the signal output terminal (9) is ■O1. Let the feedback system of the system 5) be, l
When the transfer function of the Hi extension circuit (3) is G, equations (1) and (2) hold true.

VO=Vl -V2 = (1-K)Vl...■
V 1 = Vi + G V 2 = Vi 10 K G V 1- (li ■, When vl is deleted from the equation 0, the relationship of the equation (■) is established between the input and output.

■The transfer function of formula is expressed by formula 0...■ Formula 0 is f wt-n e r if n is a positive integer.
Similarly to FIG. 2, part b shows a comb-shaped filter in which the abdomen is formed at an integer multiple of the horizontal frequency. At this time, the signal level of section a is 1 and is unrelated to the value of K. Therefore, even if the value of is varied, the second
The signal amplitude normalization circuit (7) shown in the figure becomes unnecessary.

Note that the coefficient of the coefficient unit (5) can be arbitrarily set from the outside.

In the above embodiment, a Y-shaped comb filter was described in which the abdomen is located at an integer multiple of the horizontal frequency and the comb section is located at an odd multiple of the horizontal frequency. 1) is the signal to be subtracted, and the IH, l extension circuit (
If it is configured with a subtraction circuit that subtracts the output signal of 3) as a subtraction signal, it is easy to infer that it will become a C-shaped comb filter with comb parts at integral multiples of the horizontal frequency and abdomens at odd number multiples. It is clear that the same effect as the above embodiment can be achieved.

[Effects of the Invention] As described above, according to the present invention, since the cyclic delay signal input is obtained from the output of the system, there is no need for a signal amount normalization circuit, and the system number of the system can be easily varied. A circulating comb filter is obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a comb filter according to the present invention, and FIG. 2 is a block diagram showing a conventional comb filter. (1)...Video signal input terminal, (2)...Arithmetic circuit, (3)...IH delay circuit, (5)...Mathometer, (
8)...Subtraction circuit, (S)...Signal output terminal. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Figure 1 Figure 2 Procedural amendment (voluntary) 6ki724 Showa Month Japan

Claims (4)

[Claims] (1) A video input signal is applied to a first input terminal of an arithmetic circuit having two inputs, and the output of the arithmetic circuit is applied to an input terminal of a series generator and an input terminal to be subtracted of a subtraction circuit having two inputs, respectively. The output of the multiplier is connected to the subtraction input terminal of the subtraction circuit and the input terminal of one horizontal time delay circuit, and the output of the one horizontal time delay circuit is connected to the second input terminal of the arithmetic circuit. A comb filter connected to the subtractor circuit and configured to obtain an output signal from an output terminal of the subtraction circuit. (2) The comb filter according to claim 1, wherein the arithmetic circuit is an adder circuit that adds two inputs. (3) The arithmetic circuit uses the video input signal as the signal to be subtracted, and 1
The comb filter according to claim 1, which is a subtraction circuit that subtracts the output signal of the horizontal time delay circuit as a subtraction signal. (4) The comb filter according to claim 1, wherein the coefficient of the coefficient unit can be arbitrarily set from the outside.