JPS63269893A - Drop out correcting circuit - Google Patents

Abstract

PURPOSE:To reduce the quantity of a hardware by guiding out a video signal from which a chrominance signal is removed by the use of a chrominance signal separating circuit for constituting a chrominance signal phase inversion circuit. CONSTITUTION:A chrominance signal phase inversion circuit 20 inverts the phase of the chrominance signal dislocated by 180 deg. for every 1H with respect to an input video signal, thereby, the video signal before 1H can be used as the drop out correcting signal of the input video signal. A few circuits are added to a chrominance signal separating filter 201 and used, thereby, a function for guiding out a chrominance signal removing output can be provided in a drop out correcting circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dropout correction circuit in recorded information reproducing apparatuses such as video disc players and VTRs.

BACKGROUND ART In recorded information reproducing apparatuses such as video disc players and VTRs, in order to make the system more compact and cost-effective, it is desired to reduce the hardware load of the entire system, even in the circuit system.

The present invention has been made in view of the above-mentioned points, and has the function of deriving a video signal from which color signals have been removed, thereby making it possible to reduce the hardware Φ of the entire system. The purpose of this invention is to provide an out correction circuit.

The dropout correction circuit according to the present invention includes a color signal phase inversion circuit that inverts the phase of a color signal included in an input video signal, and a color signal separation circuit that constitutes the color signal phase inversion circuit. The structure is such that the removed video signal is also derived.

Example Hereinafter, practical examples of the present invention will be explained in detail based on the drawings.

FIG. 1 is a block diagram of a recorded information reproducing apparatus having a dropout correction circuit according to the present invention and having a configuration in which, for example, signal processing is performed digitally.

In the figure, an FM video signal read from a recording medium such as a video disk is supplied to an A/D converter 2 via an analog LPF (low pass filter) 1. LPF
l is for removing aliasing distortion in A/D conversion. The digitized FM video signal output from the A/D converter 2 is supplied to a digital BPF (band pass filter) 3. This digital BPF3
extracts only the components necessary for detecting the video signal from the A/D conversion output that also includes the FM audio signal, and supplies the extracted components to the FM detection circuit 4 at the next stage. As the FM detection circuit 4, for example, one having the configuration proposed by the present applicant in Japanese Patent Application No. 59-262481 can be used.

From the detection output of the FM detection circuit 4, only the baseband component of the video signal is extracted by the video LPF 5.

A dropout detection circuit 6 for detecting a dropout of the video signal is provided, and the circuit 6 has, for example, a level comparator configuration, and is configured as a square of the envelope component of the digitized FM video signal in the FM detection circuit 4. It detects that the signal level of the signal is below a predetermined value and outputs a dropout detection signal. The digitized video signal that has passed through the video LPF 5 is supplied to a dropout correction circuit 7 and a signal valve m circuit 8. The dropout correction circuit 7 performs dropout correction in response to the dropout detection signal supplied from the dropout detection circuit 6, and also derives a video signal from which color signals have been removed, as will be explained in detail later. It also has functions. The video signal from which the color signal has been removed is passed through the synchronization signal separation filter 9, thereby attenuating high-frequency components and making the signal suitable for separating and extracting a synchronization signal such as a horizontal synchronization signal.

The signal separation circuit 8 separates and extracts the color burst signal contained in the digitized video signal, and also separates and extracts a synchronization signal such as a horizontal synchronization signal from the output signal of the synchronization signal separation filter 9 to generate a clock generation circuit 10. supply to. The clock generation circuit 10 generates 4fsc (4fsc) based on the color burst signal or horizontal synchronization signal from the signal separation circuit 8
fsc is the subcarrier frequency) and 4Nfsc (N
is an integer greater than or equal to 2, for example, it generates a clock of 3), and PLL (phase/['' tract loop)
It has a circuit configuration. The 4fsC and 4Nfsc clocks generated here are used as clocks for digital signal processing, and the sampling clock of the A/D converter 2 and the clock for signal processing up to the video LPF 5 are set to 4Nfsc, and the output from the video LPF 5 is 4fs
Downsample to the clock of c.

The digitized video signal output from the dropout correction circuit 7 is loaded into the buffer 7 memory 12 by a 4fsc clock generated by the clock generation circuit 10 based on the color burst signal extracted from the reproduced video signal. Reading of data from this buffer memory 12 is performed by 4rSC(
1) This is done by the W quasi-clock. In this way, by reading data from the buffer 7 memory 12 using a stable reference clock that is unrelated to the reproduced video signal, jitter (time axis fluctuation) of the reproduced video signal can be reduced.
can be absorbed. The digitized video signal read from the buffer memory 12 is converted into an analog signal by a D/A (digital/analog) converter 13 and becomes a reproduced video output.

FIG. 2 is a block diagram showing one embodiment of the dropout correction circuit 7 according to the present invention. In the figure, the digitized video signal is supplied to a color signal phase inversion circuit 20 and also serves as one input of a selection circuit 21. The color signal phase inversion circuit 20 includes, for example, a color signal separation filter 201 that separates and extracts color signal components from an input video signal, and a color signal component separated by this separation filter 201 that is doubled (with a coefficient of 2).
) (Actually, multiplication is performed by shifting one bit to the MSB side) 202 and the output of this multiplier 202 are passed through a separation filter 201 with the same delay time d as the color signal component.
and a subtracter 203 that subtracts the delayed video signal by the amount of time, and a video signal in which the phase of the color signal is inverted is derived as the output of the subtractor 203, and the color signal is removed by the action of the color signal separation filter 201. The configuration is such that it also derives the video signal.

FIG. 3 shows an example of the circuit configuration of the color signal separation filter 201, and FIG. 4 shows its equivalent circuit and spectrum of each part. The color signal separation filter 201 is (1/4H1
a first filter F+ having a transfer function of -Zda)2;
It has an FIR type bandpass filter configuration in which a second filter F2 having a transfer function of (1/4)(1+Z') is connected in cascade, and the input video signal is processed by delaying the color signal output which is the filter output. The video output ("M extended output") delayed by a time equal to the time and the color signal output can be taken out at the same time, and the first filter F+
A video signal from which the color signal has been removed (color signal removed output) is generated by adding the wideband color signal that is the output of the color signal and the video signal delayed by the same amount of time as this color signal to an adder. .

Since the two inputs of adder A have opposite phases, this is equivalent to subtracting the wide Wl range color signal from the delayed video signal. The operating clock frequency of the circuit is four times the frequency (4fsc) of the color subcarrier (fsc), D is a delay circuit that delays the input signal by one clock, and 24 is a multiplication coefficient (to the LSB side). 1 bit shift).

Here, the reason why a wideband color signal is used is to increase the attenuation near 'f'sc of the color signal removal output.If this is not necessary, the color signal that is the output of the second filter F2 The signal output may be subtracted from the original video signal. In FIG. 5, which shows another example of the circuit configuration of the color signal separation filter 201, the color signal is not subtracted from the original video signal, but in this way, the signals inside the filter are appropriately combined. It is also possible to derive a video signal from which the color signal has been removed by performing the following.

The video signal whose color signal phase has been inverted in the color signal phase inversion circuit 20 is basically converted to 1l-((H
: horizontal scanning period) and becomes another input to the selection circuit 21 after being delayed by a corresponding amount. The delay circuit 22 basically performs a delay equivalent to 1H, but since the input video signal has already been delayed by the time d in the color signal separation filter 201 in the color signal phase inversion circuit 20, (
A delay time of 1H-d) is set. Selection circuit 2
1 selects the video signal (side b) that is normally supplied directly, and when a dropout occurs, the video signal is passed through the delay circuit 22 in response to the dropout detection signal supplied from the dropout detection circuit 6 in FIG. ” Previous video signal (
The configuration is such that side a) is selected.

In other words, since the video signal from one day ago has a strong correlation with the input video signal, by inverting the phase of the color signal, which is shifted by 180 degrees every 1 to 1, the video signal from 1H before is dropped from the input video signal. It can be used as an out correction signal. Color signal phase inversion circuit 20 and delay circuit 2
Since the video signal that has passed through the selection circuit 21 is such a correction signal, when a dropout occurs, the selection circuit 21
By selecting this signal, it is possible to obtain a dropout-corrected video signal.

Furthermore, in the present invention, by using the color signal separation filter 201 constituting the color signal phase inversion circuit 20, the dropout correction circuit 7 is also provided with a function of deriving a color signal removal output, so that the entire system is improved. The hardware costs can be reduced. In other words, a pre-processing low-pass filter for separating and extracting the 191 signals from the video signal requires a configuration as shown in FIG. 6, but in the present invention, the color signal separation filter By adding some circuits to 201 (one adder in the example in Figure 3, one subtracter in the example in Figure 5), it is possible to derive a video signal from which the color signal has been removed. By simply using a simple filter as shown in FIG. 7 as the synchronization signal separation filter 9 in FIG. 7, filter characteristics equivalent to those shown in FIG. 6 can be achieved, and as a result, the amount of hardware for the entire system can be reduced.

FIG. 8 is a block diagram showing an embodiment of the present invention, in which parts equivalent to those in FIG. It has a set configuration.

That is, the configuration is such that a color signal is derived from the video signal after dropout correction, and this video signal is fed back to the selection circuit 21 via the delay circuit 22.

According to this, since the video signal from which the color signal has been removed is also subjected to dropout correction, it is possible to suppress disturbance of the color burst even if dropout occurs. Also, the dropout correction signal is fed back to the delay circuit 2 again.
2, so even if a dropout occurs at the same position in a plurality of consecutive horizontal scanning lines, it can be reliably corrected.

In each of the above embodiments, a case has been described in which the present invention is applied to a system in which signal processing is performed digitally, but the present invention can also be applied to a system in which signal processing is performed in an analog manner. However, since digital circuits can accurately perform processing such as multiplication, addition/subtraction, and delay, the present invention is particularly suitable for systems in which signal processing is performed digitally.

As described above, the dropout correction circuit according to the present invention includes a color signal phase inversion circuit that inverts the phase of a color signal included in an input video signal. The configuration also uses a color signal separation circuit to derive a video signal from which the color signal has been removed. Since a pass filter can be configured, the amount of hardware required for the entire system can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of a recorded information reproducing apparatus having a dropout correction circuit according to the present invention, FIG. 2 is a block diagram showing an embodiment of a dropout correction circuit according to the present invention, and FIG. The figure is a block diagram showing an example of the circuit configuration of the color signal separation filter in Figure 2, Figure 4 is a block diagram showing the equivalent circuit of Figure 3, and Figure 5 is the circuit configuration of the color signal separation filter in Figure 2. Figure 6 is a block diagram showing the circuit configuration when a low-pass filter for preprocessing for synchronization separation is configured alone, and Figure 7 is a block diagram showing another example of synchronization signal separation in Figure 1. FIG. 8 is a block diagram showing an embodiment of the dropout correction circuit according to the present invention. Explanation of symbols of main parts

Claims (5)

[Claims] (1) A color signal phase inversion circuit that inverts the phase of the color signal included in the video signal, a delay circuit that delays the video signal output from the color signal phase inversion circuit by a predetermined time, and a color signal phase inversion circuit that inverts the phase of the color signal included in the video signal. a selection means for receiving a first video signal and a second video signal which is an input signal as two inputs and selecting and outputting the first video signal when a dropout occurs; The video signal includes a color signal separation circuit that separates a color signal component from the video signal, and subtraction means that subtracts the color signal component separated by the color signal separation circuit from the video signal, and also derives a video signal from which the color signal has been removed. A dropout correction circuit characterized in that it is configured to perform. (2) The color signal phase inversion circuit uses the second video signal as an input signal.
Dropout correction circuit described in section. (3) The dropout correction circuit according to claim 1, wherein the color signal phase inversion circuit uses the output signal of the selection means as an input signal. (4) The dropout according to claim 1, wherein the delay circuit has a delay time that is the delay time in the color signal phase inversion circuit subtracted from a time equivalent to 1H (H: horizontal scanning period). correction circuit. (5) The color signal phase inversion circuit is characterized in that, together with the color signal separation circuit, the color signal phase inversion circuit includes a subtracter that subtracts a signal obtained by doubling the color signal component separated by the separation circuit from the input video signal. A dropout correction circuit according to claim 1.