JPS6235782A - Comb line filter - Google Patents

Abstract

PURPOSE:To eliminate the need for a signal quantity normalizing circuit, to easily vary the coefficient of a coefficient multiplier, and to prevent a false signal from being generated by cutting of a circulation signal unless there is vertical correlation while obtaining the circulation signal from the output of the coefficient multiplier. CONSTITUTION:A circulation delay signal input is obtained from the output of the coefficient multiplier 5 to eliminate the need for the signal quantity normalizing circuit and a killer circuit 9 is provided in a circulation loop to prevent a false signal from being generated. The signal quantity normalizing circuit is unneeded, so the desired degree of SN ratio improvement is obtained by varying only the coefficient K of the coefficient multiplier 5 without any variation in signal quantity. Further, the killer circuit 9 cuts off the circulation loop of the signal unless there is vertical correlation, thereby suppressing the generation fo a false signal.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a comb filter, and particularly relates to the configuration of a circulating comb filter used for improving the signal/noise (SIN) ratio of a video signal. .

[Conventional technology]

Circulating comb filters are used to improve the S/C ratio of video signals. -As an example, Figure 2 shows NHK in April 1962.
The circulating comb filter described in the Giken monthly report “Video signal process and image quality using comb filter” is shown.
/N ratio improvement operation will be explained. In Figure 2, (
1) is a video signal input terminal, (2) is an arithmetic circuit, (3) is a one horizontal time (abbreviated as IH in the following explanation) delay circuit, (4) is an addition circuit, (5) is a multiplier, ( 6) is a signal output terminal, (7) is a signal amount normalization circuit, and (8) is a normalized signal output terminal.

The missing number operation will be explained. Now, video signal input terminal +
The signal of 1) is Vi, and the input signal of IH delay circuit (3) is v.
The signal of the H1 signal output terminal (6) is set to Vo, and the
) is the feedback system number K, and the transfer function of the IH delay circuit (3) is G.
If so, equations [1] and [2] hold true.

VH-Vi=KVo...=・[13Vo=
Vi ” GVH--[2](x) From equation (2), when vH is eliminated, the output signal V is obtained.

The relationship between the input signal Vt and the input signal Vt is expressed by equation [3].

■. =1+G, yo. Vi...--[3] 1+G In equation [3], -' is the transfer function of the filter in Figure 2, and the transfer function G of the IH delay circuit is, when dealing with television signals with large line correlation, Let τL = 1/11 (f is the line frequency).

1 ′″jωτ = LJ = e 1CO1k+3f, -jliln
It is expressed as ωr.

Therefore, the transfer function of equation [3] can be expressed as equation [4].

When n is a positive integer, formula [4] becomes when f=nf1,
7. `` ' = ``'''') When f This shows that the degree of S/N ratio improvement can be freely set because the sharpness of the amplitude-frequency equality of the filter changes.

In addition, since the signal Vo at the signal output terminal (6) is a function of K, the signal amount normalization circuit (7) multiplies Vo by (1-K), so that the normalized signal output terminal (8) It is provided in order to output a signal that does not involve a change in output amplitude due to a change in K.

[Problem that the invention seeks to solve]

In the case of conventional circuits, when the coefficient K of the multiplier is changed in order to change the degree of improvement of the S/N ratio, the multiplier of the signal amount normalization circuit must also be changed in proportion to K. Difficult to achieve consistency.

It has been difficult to substantially vary K. Furthermore, when a video signal without vertical correlation is input, there is a problem that a false signal is generated.

This invention was made in order to solve the above-mentioned problems, and provides a circular filter circuit in which the coefficient K of the coefficient generator can be easily changed, and in which no false signals are generated. [Means for Solving the Problems] The cyclic comb filter according to the present invention takes the cyclic delay signal input from the output of the multiplier.

This eliminates the need for a signal amount normalization circuit, and a killer circuit is provided in the circulation loop to prevent the generation of false signals.

[For production]

With this invention, the signal amount normalization circuit is not required, so by changing only the coefficient of the coefficient generator, the desired S/N ratio [Yukiyuki degree is 1d] can be achieved with a change in the amount. You can get it without asking. Furthermore, if the vertical correlation is low, a killer circuit interrupts the signal circulation loop to suppress the generation of false signals.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, (1) is a video signal input terminal, (2) is an arithmetic circuit, [3] is an IH delay circuit, (5) is a multiplier, and (9)
1 is a killer circuit, (10 is a subtraction circuit, and (b) is a signal output terminal. 1 and 1, the same symbols are used for parts in FIG. 1 that are equivalent to those in FIG. 2.

Next, the operation will be explained. Now, when a video signal with vertical correlation is input, the killer circuit (9) acts as a buffer and does not affect the signal in any way.

At this time, if the signal of the video signal input terminal (1) is vi, the output signal of the killer circuit (9) is vl, the output signal of the multiplier (5) is v2, and the output of the signal output terminal (b) is Vo, Equations [5] and (6) hold true.

Vo = V, -V, = (1-K)V, -・
・−・−(5]V, == Vl 4 GV, ==
Vi + KGV, ・−・−・・[6)(5],
[If vI is deleted from equation 61, the input/output relationship becomes
[7] Formula holds true.

Vo - Nijikan Vi ...... [7] 1-KG The transfer function of equation [7] is (1-K)/(1-KG), which can be expressed as equation [8]. It will be done.

[8] Equation shows that the invasion number and deviation for which n is positive is 1 when f = nf1, and (1-K when f = (n++/x)fI).
)/(14K), which is the same as the filter in Figure 2 (, indicating that it is a comb-shaped filter with a belly at an integer multiple of the line frequency.When f=nfz, the signal level is 1 is independent of the value of K, so even if the value of K is varied, a signal amplitude normalization circuit is not required.

Next, consider the case where a video signal without vertical correlation is input. At this time, the above-mentioned formulas [5] to [8] are satisfied, and a false signal is generated. Once upon a time.

If there is a vertical correlation or something like f, use the killer circuit (9).

If the feedback loop formed by the multiplier (5) and the IH delay circuit (3) is cut off, the signal input from the signal input terminal (1) is not output to the signal output terminal Ql). , no false signals are generated.

In the above embodiment, a Y-shaped comb filter is described in which a comb portion is formed at an integral multiple of the line frequency or at an odd multiple of the line frequency. If the output of the lH delay circuit (3) is subtracted from the signal at the signal input terminal (1), a C-shaped comb filter will be created, with comb parts at integral multiples of the line frequency and abdomens at odd number multiples. This can be easily inferred from the structure of the filter according to the present invention 1, and it is clear that the same effect as the above embodiment is achieved.

〔Effect of the invention〕

As described above, according to the present invention, a cyclic signal is obtained from the output of the multiplier, and at the same time, when there is no vertical correlation, the cyclic signal is cut off (since the square filter is configured, the signal amount is normalized). No circuit required.

A circulating comb filter can be obtained in which the system number can be easily varied and at the same time, no false signals are generated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a comb filter according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional comb filter. In Figure 2, C1) is a video signal input terminal, (2) is an arithmetic circuit, (3) is an IH delay circuit, [5] is a multiplier, and (9)
0 is the killer circuit, αQ is the subtraction circuit, and (b) is the signal output terminal.0 Note that the same symbols in the figures indicate the same or equivalent parts.

Claims (5)

[Claims] (1) An arithmetic circuit to which a video input signal is input to the first input terminal, a killer circuit to which the output of this arithmetic circuit is input, a multiplier to which the output of this killer circuit is input, and an output of this multiplier to 1 a horizontal time delay circuit that delays the horizontal time and supplies the signal to a second input terminal of the arithmetic circuit; and a subtraction circuit that subtracts the output of the multiplier from the output of the killer circuit to obtain a desired filter output signal. A comb-shaped filter characterized by: (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
2. The comb filter according to claim 1, wherein the comb filter 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 any one of claims 1 to 3, characterized in that the coefficient of the coefficient generator can be arbitrarily set from the outside. (5) The comb according to any one of claims 1 to 4, wherein the killer circuit is configured to attenuate or cut off the output signal of the filter by a predetermined control signal. filter.