JPS63100808A - Comb-line filter circuit - Google Patents

Abstract

PURPOSE:To improve the picture quality by using the least quantity of subtraction in the color burst signal period than other periods and using the largest quantity of delay in the color burst signal period more than that of the other periods. CONSTITUTION:A comb-line filter 21 and a hue variable device 22 are provided to a reproducing chroma system. The comb-line filter characteristic of the feedback comb-line filter 21 is varied with the color burst signal period and the other periods. That is, a constant K is decreased in the color burst signal period and the constant K is increased in the other periods. As a result, the improvement of the S/N is less in the color burst signal period but the time delay in the APC system is less, the response of the APC is not deteriorated, while the S/N is improved in the periods other than the color burst signal period because of the adoption of correlation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a feedback comb filter circuit for removing adjacent signals of a reproduced chroma signal system of a magnetic recording/reproducing apparatus (hereinafter referred to as a VTR).

[Conventional technology]

The VTR playback system is called ``home video technology.''
(April 20, 1980, Japan Broadcast Publishing Association 194).

Figure WIJ2 shows a reproduction signal processing circuit for reproducing color signals. The color signal converted to a low frequency is detected from a magnetic tape (not shown) by a magnetic head 1, amplified by a preamplifier 2, extracted by a low pass filter (LPF) 3, and subjected to frequency conversion. added to circuit 4.

Since the frequency conversion circuit 4 receives the intermediate signal fc, a band pass filter (BPF) 5 extracts the difference frequency component, and an ACC circuit 6 controls the signal level. This signal is reduced by the burst signal reduction circuit 7 by 6 dB. As a result, since only the burst signal is increased by 6 dB during recording, it becomes the original carrier color signal.

Next, in order to improve the signal-to-noise ratio of the signal, an adder 10 mixes the luminance signal that has passed through a comb filter 8 and a luminance signal reproduction processing circuit 11 to reproduce a video signal at an output terminal 12. Ru.

Here, a signal processing circuit that creates a carrier signal fc for correcting time axis fluctuations of color signals will be described. A voltage controlled oscillator (VCO) 16 generates a burst signal in the reproduced signal from the comb filter 8 output and a 3.58
MH! The error voltage obtained by comparing the output signal of the crystal oscillator 14 oscillating with the phase comparison i (P, C') 13 shall be controlled. Its oscillation frequency is 160 f
Frequency 160fu and Δ corresponding to the above error voltage with u as the center
It becomes f. The output signal of the VCO 16 is divided into 1/2 by the frequency dividing circuit 17.
The frequency is divided into four and input to the frequency conversion circuit 18. Then, the frequency is converted using the signal fs from the crystal oscillator 14, and the sum frequency component is converted into a Bantepayu filter (BPF).
C taken out from 19.

A carrier signal fc is obtained by being applied to the frequency conversion circuit 4.

Now, the magnetic head 1 is also being reproduced, and the color signal that has passed through LPF 3 is waiting for time axis fluctuation, and its frequency is -4-
If fa, the carrier color signal outputted to the BPF 19 will be fs, and the time axis fluctuation component -Δf will be removed.The carrier signal fc or fc = 4Of)1-)--Δf
-1-fs, the oscillation frequency of the VCO 16 must be -1-fs. This VC016 is the output fs of the crystal oscillator 14
=”h The reference signal of 58 FLHz and the reproduced carrier color signal σ) burst signal are compared in phase by P and C15, and controlled by the error signal.

By the way, in order to perform phase comparison only on the color burst signal portion, the color burnout gate pulse generator 20 generates a color burst gate pulse from the horizontal synchronization signal of the luminance signal, and Cl5KX1 is generated.

The signal flow has been explained above, but from the perspective of improving 8/N, two types of measures have been taken.

(1) Upgrading the color burst signal level When recording, the color burst signal is boosted twice and recorded, and when played back, it is multiplied by 1/2 and returned to the original signal before being extracted.

Since the influence of noise is reduced by half, 87N can be improved by several das.

(2) < Use of L-type filter Remove crosstalk of low-frequency converted chroma signal. In order to increase its effectiveness, there is also a feedback comb filter whose characteristics can be varied depending on the correlation between lines.

Here, we will briefly discuss the feedback<C type filter, which is the core of the present invention.

FIG. 3 shows a block diagram of the feedback comb filter 8, and FIG. 4 shows its frequency characteristics and delay time characteristics. 6th
In the figure, 52 is a delay line whose delay time is 6 & 5 μsec for one horizontal signal period.

51 and 35 are subtracters, and 64 is an adder. 55 is an attenuator, and the adder 64 and the subtracter 51 constitute a feedback system.

The transfer function from the input terminal 30 to the output terminal 56 is expressed by the following equation, where K is the feedback amount of the attenuator 53.

T = 6 & 5 μsec, g = j
ω Therefore, its frequency characteristics are shown in FIG. 4(a).

Further, the delay time characteristics are shown in FIG. 4(b).

In other words, as K increases, the comb characteristics become steeper.
The noise part will be removed and an improvement of 8/N will be obtained.

However, as can be seen from FIG. 4(b), as K increases, the delay time increases. By the way, the comb filter is APC.
It's in the loop. As a result, if K is a dog, then APe
Due to the presence of delay elements in the loop, the response of the human PC becomes slow. Therefore, the value of K must be determined by considering the S/N and APC response, and there is a problem that PM 8/N cannot be sufficiently improved by simply increasing K.

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the invention is to provide means that can sufficiently improve Pki8/N when a feedback comb filter is used.

[Means of solving the problem]

In order to achieve the above object, the present invention optimizes the APC response by changing the characteristics of the color burst signal part and the video signal part used for APC.
The aim is to ensure the improvement effect of For this purpose, as shown in FIG.
2 will be established.

The characteristics of the comb filter of the feedback comb filter 21 are shown in Figure 5 in the color burst signal period and other periods.
to become In other words, during the color burst signal period, KY
In other cases, K is made thicker.As a result, the improvement of 8/N is small in the color burst signal period, but the AP
Since the time delay in the C system is small, the response of APe does not deteriorate. Since correlation is taken during periods other than the color burst signal period, an improvement in S/N can be obtained.As mentioned in the conventional example, the color burst signal is boosted twice when recording, and when recorded again, it is restored as before. Nishimata takeout 1, -me S/N) 1 was originally a few clB compared to other than Ecolor Burst Shinji. Therefore, in the 1-power error burst signal period, the is/Ni is improved to P overall by focusing on the response of AP(?) rather than the S/N.

By the way, in the method described above, the delay time changes between the color burst signal and other signals, so the hue changes. Therefore, the hue variable device 22 adjusts the delay time so that it does not change between the multi-burst signal period and other periods.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIG. Second
The following two points differ from the diagram.

(1) A color burst gate pulse is applied to the feedback comb filter 21 from the color burst gate pulse generator 2o.

(2) A color burst gate pulse is applied from the color burst gate pulse generator 2o to the hue adjuster 22 (upstream of the adder 10).

First, (1) will be explained using FIG.

In Fig. 5, attenuators 37 and 58 have different feedback amounts by 1°K2.
is set to The changeover switch 59 is controlled to be 1 or less according to the color burst gate pulse.

In addition to the color burst signal period, 1 = 1 (Large delay time) Color burst signal period K2 = O < Small delay time) As a result, in the color burst signal period related to APC, the delay time delay is small, so the APC response slows down almost nothing. None.

However, since the delay time changes between the color burst signal period and other periods, the hue changes.

Correct it using (2). Next, (2) the sixth
Explain using diagrams.

In FIG. 6, 41 is a low pass filter (LPF) whose delay time is set to the difference between 1 and 2 as described above. Then, it is controlled by the changeover switch 42 as follows.

Other than the color burst signal period, no LPF (small delay time) Color burst signal period, with LPF (large delay time) Here, the delay time of LPFal is set to correct the delay caused by the feedback comb filter.

An example thereof is shown in FIG. 7G. The LPF 41 is configured by a resistor 44 and a capacitor 45. One color burst gate pulse is applied to the terminal 47. During the color burst signal period, the color burst gate pulse is high (High).
h), the l transistor 46 becomes operational. Therefore, during the color burst signal period, the signal input to the terminal 40 passes through the LPF. For other periods,
Since the transistor 46 is active, the "I" signal is not delayed.

Note that since the LPF 41 is located outside the APC loop, the delay time changes between the color burst signal period and other periods, but the response of the APC is not affected.

With (1) above, the APC response does not deteriorate, and with (2), the hue is corrected. (1) and (2)
), the color burst signal and the color burst signal (delay times other than 1 are the same. As a result, P without any change in hue
An improvement in MS/N is obtained.

In addition, in the above explanation, K = O except during the color burst signal period, but if the S/N of the signal is poor, the value of K can be increased, and even if the APC response is sacrificed, the overall S It is also possible to improve /N.

In short, in the chromaticity signal low-pass conversion recording method that doubles the color burst signal during recording and restores it to its original state during playback, the value of K is changed between the color burst signal and other periods. It is sufficient to use means for improving the PMS/N and correcting the change in hue caused thereby.

〔Effect of the invention〕

As described above, according to the present invention, when the feedback comb filter is used, it is possible to sufficiently reduce the 8/N, P of the ROMA signal.
An improvement in MS/N can be obtained, which has a significant effect on improving image quality.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing a reproduction chroma signal processing system of a conventional VTR, and Fig. 3 is a feedback diagram used in a reproduction chroma signal processing system of a conventional VTR. A block diagram of a comb filter. Fig. 4 is a characteristic diagram showing the frequency characteristics and delay time characteristics of a feedback comb filter used in the reproduction chroma signal processing system of a conventional VTR. Fig. 5 is a feedback diagram of the present invention. FIG. 6 is a block diagram of the comb filter, FIG. 6 is a block diagram of the hue adjuster of the present invention, and FIG. 7 is a circuit diagram showing an example of the hue tone H of the present invention. 7...Burst signal reduction circuit. 20...Color burst gate pulse generator. 21...Feedback comb filter. 22... Hue adjuster. 67...Attenuator. 68...Attenuator. 69... Selector switch. 41...LPF. 42... Selector switch.

Claims (1)

[Claims] A chromaticity signal low-pass conversion recording method that records a color burst signal twice and restores it to its original state upon playback,
The signal before and after the 1H (horizontal period) delay line in the APC loop is subtracted to attenuate the added component of the input and output of the delay line of the comb filter circuit that passes the chromaticity signal component. In a feedback comb filter provided with a feedback system for subtracting from an input signal in a subtracter located at the front, a first means for making the amount of subtraction in the subtracter smaller in a color burst signal period than in other periods; A feedback comb filter circuit comprising a second means for increasing the amount of delay during a color burst signal period compared to other periods by means of a delay circuit provided outside the loop.