JPH0348592A - Drop out compensation circuit - Google Patents

Abstract

PURPOSE:To reduce the delay quantity of a signal in a low-pass area and to inexpensively improve picture quality by providing a chroma trap circuit on a delay line including a delay element. CONSTITUTION:A signal PB-C is mixed with a signal sent via the output side terminal 3c of a DOC(drop out correction) switch 3 controlled with a DOC detection circuit 3A via an adder 7, and is sent to a voltage controlled type variable gain amplifier VCA 9 via the delay line 8 using a charge coupled device(CCD), and gain loss due to the CCD delay line 8 is compensated. The macro trap circuit 10 is arranged at the rear stage of the delay line 8, and eliminates a chroma signal component. Thereby, the delay line 8 can be used in common with the delay line for comb-line filter in a reproducing signal system, and also, no LPF for DOC is required at the rear stage of the delay line, which reduces the delay quantity of the signal in the low-pass area. Therefore, the image can be inexpensively improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The details of the dropout compensation circuit of the present invention will be explained according to the following items.

A. Industrial field of application B0 Overview of the invention C0 Prior art [Figure 2] D1 Problem to be solved by the invention [Figure 3] E1 Means for solving the problem F. Example [Figure 1 Effects of the invention (A. Field of industrial application) The present invention relates to a novel dropout compensation circuit. Specifically, this is a dropout compensation circuit in which the circuit can be constructed using the same delay line for multiple comb filters (for example, luminance signals and chroma signals) as the delay line for the dropout compensation circuit. This is a new technology that improves the performance of the dropout compensation circuit by reducing the amount of delay in the low frequency range of the signal by providing a trap circuit on the delay line, and also achieves this at a low cost. The purpose of this invention is to provide a dropout compensation circuit that provides a reliable dropout compensation circuit.

(B. Summary of the Invention) The dropout compensation circuit of the present invention includes a delay element that is shared with a delay element of a comb filter and has a delay output of -, and an AG for compensating for gain loss due to the delay element.
This is a dropout compensation circuit equipped with a C circuit, and by providing a chroma trap circuit on a delay line that includes a delay element, the amount of signal delay in the low frequency range of the signal is reduced, and image quality can be improved at low cost. It was made so that it could be done.

(C, Prior Art) [Figure 2] In a system in which one tree of delay lines is shared as a delay line for multiple comb filters, a custom IC delay element with multiple delay outputs is used. Often,
- An example is shown in Japanese Patent Application Laid-Open No. 62-164398.

In this case, as shown in FIG.
Let it be o2. ), one of them S01 is the human signal (S+
shall be. ) is given a delay amount (this is α), and the other 302 is the input signal S! A delay amount of IH (one horizontal scanning period) + α is given to the signal, and by taking the difference between the two in a comb filter, a delayed output delayed by exactly IH can be obtained. At the same time, a delay output (Sooc) for DOC (dropout compensation) is also created in ■Ca, and the delay amount in this case is a different value from the above-mentioned delay amount (
Let this be β. ), and with respect to the human signal S, IH
The signal is output as a signal delayed by −β, and unnecessary (chroma) components are removed via a low-pass filter b provided at the subsequent stage.

(D. Problem to be Solved by the Invention) [Figure 3] By the way, in the above circuit, the delayed output s ooc
Since the signal is passed through the low-pass filter b, the amount of delay in the low frequency range of the signal increases, leading to a decrease in the performance of the DOC circuit. For example, as schematically shown in Fig. 3, When playing back a video signal e in which a black (diagonal line) vertical line d is drawn on the TV screen C, if a dropout of several H minutes occurs for some reason (arrow f ), the amount of signal delay accumulates, and the black portion on the scanning line at that time shifts diagonally, resulting in distortion on the screen.

Furthermore, regarding delay ICs, the amount of delay associated with the DOC delay signal is different from that of the comb filter delay signal, which leads to circuit complexity and an increase in IC cost, resulting in an increase in product cost. There are problems like this.

(E. Means for Solving the Problems) Therefore, in order to solve the above-mentioned problems, the dropout compensation circuit of the present invention has a delay element that is commonly used as a delay element of a comb filter and has a delay output of -. , and an AGC circuit for compensating for gain loss due to the delay element, and a chroma trap circuit is provided on a delay line including the delay element.

Therefore, according to the present invention, by using a trap circuit in place of the conventional low-pass filter for DOC, the amount of delay in the low frequency range of the signal can be reduced, and moreover, the same delay output can be achieved with the comb filter. Since the delay line can be shared, the circuit can be constructed at low cost.

(F. Embodiment) [FIG. 1C Below, details of the dropout compensation circuit of the present invention will be explained according to the illustrated embodiment. The illustrated embodiment uses the dropout compensation circuit of the present invention to connect the delay line of the DOC circuit and the reproduced Y (luminance) signal (hereinafter rPB-YJ) in a VTR or the like.
shall be. ) and a comb filter delay line for a reproduced chroma signal (hereinafter referred to as rPB-CJ).

(a, circuit) 1 is a DOC circuit.

2 is a signal input terminal to which the signal PB-Y is input manually.

3 is a DOC switch whose switching is controlled by a DOC detection circuit 3A, one of its input terminals 3a is connected to the signal input terminal 2, and the other 3b is connected to the output terminal of a clamp circuit to be described later. It is connected. Further, the output terminal 3c is connected to a subtracter 5 via an equalizer 4.

6 is a signal input terminal, into which the signal PB-C is input, and this signal is mixed with the signal sent via the output side terminal 3C of the DOC switch 3 in the adder 7 arranged at the subsequent stage, and the CCD VCA (
voltage-controlled variable gain amplifier) 9, where CC
Gain loss due to the D delay line 8 is compensated for. A general-purpose IC is used as the CCD delay line 8, and is configured to output a - delayed signal that is given a predetermined amount of delay with respect to the input signal.

10 is f sc (color subcarrier frequency) 43.58MH
2 is a chroma trap circuit centered on CCD delay line 8, and is arranged after the CCD delay line 8, and is provided for removing chroma signal components.

Reference numeral 11 denotes a clamp circuit, which is arranged after the chroma trap circuit 10 for DC level adjustment. The output terminal of the clamp circuit 11 is connected to an AG
It is connected to one input terminal of the C detection circuit and the input terminal 3b of the DOC switch 3.

12 is an AGC detection circuit, which has signal input terminals such that one input terminal receives the delayed signal from the clamp circuit 11, and the other input terminal receives the main signal of the PB-Y signal. Connected to 2. The output of the AGC detection circuit 12 is sent as a control signal 18 to the VCA 9, thereby controlling the gain of the VCA 9. In addition, 13 is the AGC detection circuit 12
This is a capacitor inserted between the output terminal and the ground line.

A subtracter 14 subtracts the delayed signal from the main signal PR-Y and sends the output as a negative signal to the subtracter 5 via a limiter, attenuator, etc. (not shown). Then, in this subtracter 5, the signal sent from the subtracter 14 is subtracted from the output signal of the equalizer 4, and the signal PB-Y(
This is referred to as "rPB-Yco□". ) is output to the signal output terminal 15. Note that the delay signal manually input to the subtracter 14 may be input to the VCA as indicated by the broken line in FIG.
You may take it out immediately after 9.

16 is a subtracter which subtracts the signal branched after the CCD delay line 8 from the signal branched after the adder 7, and passes the signal through a comb filter to the signal output terminal 18 via a bandpass filter 17. It is designed to be output as a signal PB-C (this will be referred to as "PB-cooMIl"). Note that the VCA, clamp circuit, and AGC provided on the path from the CCD delay line 8 to the subtracter 16
The illustration of the detection circuit system is omitted.

(b. Effect) However, in the DOC circuit 1 described above, the CCD
The delay line 8 is shared with the delay line for the comb filter of the reproduced signal system, and a chroma trap circuit 10 is provided behind it, and the DOC circuit is installed after the delay line with multiple delay outputs as in the conventional case. Since there is no need to provide a special low-pass filter, the amount of delay in the low frequency range of the Y signal is reduced.

(G. Effects of the Invention) As is clear from the above description, the dropout compensation circuit of the present invention has a delay element that is shared with the delay element of the rectangular filter and has a delay output of -; This dropout compensation circuit includes an AGC circuit for compensating gain loss due to delay elements, and is characterized in that a chroma trap circuit is provided on a delay line including the delay elements.

Therefore, according to the present invention, the amount of delay in the low frequency range of the signal is reduced by using a trap circuit instead of the conventional low-pass filter for DOC, and the same delay output is obtained between the comb filter and the comb filter. Since a delay line with a delay line having a delay line having a delay line can be shared, the circuit can be constructed at low cost.

In the above embodiment, the trap circuit is a VCA.
Although an example in which the dropout compensation circuit of the present invention is placed in the latter stage is shown, the technical scope of the dropout compensation circuit of the present invention is not limited to this only, and the dropout compensation circuit may be placed anywhere on the delay line.

It is a block diagram, and FIG. 3 is a schematic diagram for explaining the problem.

Explanation of symbols 1...dropout compensation circuit, 8...delay element, 9.12...AGC circuit, 10...Chroma trap circuit applicant

Claims (1)

[Claims] A dropout compensation circuit comprising a delay element that is shared with a delay element of a comb filter and has a delay output of -, and an AGC circuit for compensating for gain loss due to the delay element. A dropout compensation circuit characterized in that a chroma trap circuit is provided on a delay line including a delay element.