JPH0440755A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To always secure the match of levels between the output and input signals by setting the gain of an amplifier so as to keep the input signal within an A/D conversion range and at the same time setting the coefficient of a transversal filter based on the gain of the amplifier. CONSTITUTION:A reference signal level detection circuit 9 estimates the maximum and minimum levels of an input video signal based on the level of a GCR signal and sets the gain of a variable gain amplifier 2 at alpha so that the input video signal is kept within an A/D conversion range. At the same time, a coefficient (1/alpha) - 1 is set at a tap where no time error is caused between both output video signals of a delay circuit 4 and a feedforward transversal filter 5. Thus the output video signal Vs of an adder 6 is set at 1/alpha of an output video signal Vdin of an A/D converter 3 and serves as an output video signal Vout. Thus the gain of a sum signal including the amplifier 2, the filter 5, and the circuit 4 is exactly equal to 1. Then both input and output video signals are set at the same level in a system as a whole.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ghost removal device that removes a ghost signal from a video signal containing ghosts.

[Prior Art] For example, when radio waves radiated from a transmitting antenna hit a structure such as a building, a mountain, etc., are reflected, and arrive at a receiving antenna, a ghost signal is superimposed on a video signal. This appears as a ghost in the image, degrading the image quality.

In order to remove ghost signals included in such a video signal, the 18th and 281st vertical retrace periods of the video signal are
The ghost removal reference signal (O
CR signal) is inserted and goes low. This GCR signal is a signal with an 8-field period, and as shown in the figure, the first, third,
In the 6th and 8th fields, the rise is 5 inches.
A G CRt<Russe waveform with X/X and falling characteristics of 2T is inserted.

O-pedestal waveforms having the same set-up level as the pulse waveform are inserted into the second, fourth, fifth and seventh fields. As shown in the figure, these two waveforms form an 8-field sequence that is sent out in reverse at an 8-field period.

Ghost removal devices using this OCR signal have been proposed in the past. FIG. 2 shows an example of this.

In the figure, 1 is an input terminal to which a video signal Vin output from, for example, a video detection circuit (not shown) is supplied, and this signal Vin is supplied to a variable gain amplifier 21, a synchronous separation circuit 17, and a clock generation circuit 19. be done.

The output signal Va of the variable gain amplifier M2 is digitized by the A/D converter N3, and the output signal Vd1n is sent to the delay circuit 4 and the feedforward transversal filter 5.
, reference signal (OCR signal) level detection circuit 9 and base
The signal (OCR signal) is supplied to the capture circuit IO.

Note that the coefficients of the feedforward transversal filter 5 and the feedback transversal filter 8 are all O at first.

At the clock generation port W819, the color carrier frequency fsc is 4.
A clock signal CK of twice the frequency is supplied to the entire system.

The synchronization separation port 'ts17 extracts the synchronization signal Syn from the input video signal (in) and supplies it to the gate signal generation circuit 18. A gate signal generation circuit 18 generates a control signal Cnt from the synchronization signal Syn, and uses it as a gate signal for capturing an OCR signal in a reference signal level detection circuit 9 and a reference signal capture circuit 10.

The reference signal level detection circuit 9 assumes the maximum and minimum values of the input video signal based on the level of the OCR signal, and performs variable gain amplification i so that the signal falls within the conversion range of the A/D conversion.
A gain α of 12 is set.

After setting the gain of the variable gain amplifier 2, the reference signal capture circuit 10 captures the line into which the GCR signal is inserted from the A/D conversion output signal Vd1n using the gate signal Cnt, and performs the following 8 Perform field calculation processing.

In other words, in the 8-field sequence shown in Figure 3, the first
, the third, sixth, and eighth fields (pulse waveform fields) are added, and the second, fourth, fifth, and seventh fields (0 pedestal waveform fields) are subtracted. Through this calculation, the synchronization signal, burst signal, previous line signal, etc. are erased, resulting in a signal GS containing only the OCR pulse waveform as shown in FIG. 4A. This signal Gs is transmitted to the difference circuit 11.

In the difference circuit 11, the input signal Gs and the signal Gs
Find the difference signal from the signal delayed by one clock, and use the signal shown in Figure 4B.
A difference signal Ds like this is output to the subtracter 12.

The reference signal generation circuit 13 generates an internal reference signal Rs as shown in FIG. 4C in synchronization with the timing of the difference signal Ds. The subtracter 12 subtracts the difference signal Ds and the internal division reference signal Rs to obtain an error signal Es, which is transmitted to the filter coefficient calculation and setting circuit 14.

The filter coefficient calculation and setting circuit 14 calculates the coefficients of the transversal filter from the error signal Es, and sets the coefficients Cf to the feedforward transversal filter 5 and the feedback transversal filter 8, respectively.
, Cb is set.

The ghost removal range, that is, the filter coefficient setting range is up to before the 2T pulse in Figure 4B, and the maximum is 44.7 μs.
It will be up to ec.

A signal Vd1n obtained by A/D converting the input video signal passes through a delay circuit 4 and a feedforward transversal filter 5, and its output signals Vd and Vf are added in an adder 6, thereby eliminating the front ghost. and nearby ghosts are removed, and the output signal VS is transmitted to the adder 7.

In the adder 7, the output V dout of the adder is passed through a feedback transversal filter 8 and converted into a signal v.
signal V do from which ghosts have been removed by adding with b
ut, and the D/A converter 15 converts the analog signal V o
It is output from the output terminal 16 as ut.

[Problem to be solved by the invention] Now, in such a conventional device, when the magnitude of the input signal is changed at the input stage, the changed magnitude becomes an error signal, so ghosts are removed. Sometimes the output level will be corrected.

However, since the correction cannot be completed until the ghost is removed after changing the gain of the input stage, the signal level is outputted at α times the input signal during that time, which affects the brightness of the screen.

In view of this, the present invention proposes a ghost removal device that solves these conventional drawbacks, and in which the level of the output signal is always the same as the level of the input signal.

[Means for Solving Problem W] In order to solve the above-mentioned problems, the present invention includes a variable gain amplifying means that amplifies an input video signal with a set gain, and an A/D converter that digitizes the output video signal. D conversion means, a transversal filter for removing ghost signals from the digital signal, and a level detection unit that detects the level of the digital input video signal and sets the gain of the variable gain amplifier and the coefficient of the transversal filter based on the detected level. a reference signal capture means for capturing a ghost removal reference signal from a digital input video signal and performing 8-field calculations; a difference means for differentiating the reference signal; and an internal reference for generating an internal reference signal in accordance with the timing of the difference signal. A/ In order for the input video signal to fit within the D conversion input range,
The gain of the variable gain amplifier is set by the output of the level detection means, and the coefficients of the transversal filter are set based on the output of the level detection means so that the level of the output video signal does not change. It is characterized by this.

[Function] When changing the gain α of the input stage amplifier 2, the coefficient of the filter 5 is set to be (1/α)-1 according to the gain α.

In this way, the level of the output signal is always the same as that of the input signal even during the period from when the gain α of the input stage is changed until the ghost is removed.

[Embodiment] Next, an example of a ghost removal device according to the present invention will be described in detail with reference to FIG. 1.

However, the explanation of the same parts as in FIG. 2 will be omitted.

In the reference signal level detection circuit 9, the maximum and minimum values of the input video signal are assumed based on the level of the OCR signal, and the gain of the variable gain amplifier 2 is adjusted to α so that the input video signal falls within the replacement range of A/D conversion. Set to .

At the same time, a coefficient (1/ Set α)-1. At this time, the tap coefficients of the other filters remain O.

When the filter coefficients are set in this way, the output image of the adder 6 is '! Vs is 1/α of the output video signal Vd1n of the A/D conversion 1l13, and this is the output video signal V
It becomes out.

Therefore, in the entire system, the sum of the gains of the variable gain increase iI2, the filter 5, and the delay circuit 4 is exactly 1, so that the input video signal and the output video signal are at the same level.

After that, the output level can be corrected when the filter coefficients are set as in the conventional case. Therefore, variable gain amplifier 2
Even after the gain is changed and the ghost is removed, the input and output levels remain the same, so the brightness of the screen does not change.

[Effect of the invention] As explained above, in this invention, the input video signal is
The gain of the amplifier provided at the input stage is changed so that it falls within the conversion range of the /D converter, and at the same time, the coefficients of the filter are set according to the gain.

According to this, since the output video signal is always at the same level as the input video signal, the brightness of the screen can be kept constant even after the gain of the amplifier of the input means is changed and the ghost is removed.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of a ghost removal device according to the present invention, FIG. 2 is a configuration diagram of a conventional ghost removal device,
FIG. 3 is an explanatory diagram of an 8-field sequence OCR signal, and FIG. 4 is a diagram of various waveforms of the ghost removal device. 8 ・ 9 ・ 10 ・ 11 ・ 13 ・ 14 ・ 15 ・ 17 ・ ・Variable gain amplifier・A/D converter・Delay circuit・Transversal filter for feedforward・・Transpersal filter for feedback・OCR signal level detection circuit・OCR signal acquisition circuit ・Differential circuit ・Reference signal generation circuit ・Filter coefficient calculation setting circuit ・D/A converter ・Sync separation circuit 18...Gate signal generation circuit Figure 3

Claims (1)

[Claims] (1) Variable gain amplification means for amplifying an input video signal with a set gain; A/D conversion means for digitizing the output video signal; and a transversal filter for removing ghost signals from the digital signal. , level detection means for detecting the level of the digital input video signal and setting the gain of the variable gain amplifier and the coefficient of the transversal filter based on the level; and a reference signal for taking a ghost removal reference signal from the digital input video signal and performing 8-field calculations. A capture means, a difference means for making a difference between the reference signals, an internal reference signal generation means for generating an internal reference signal in accordance with the timing of the difference signal, and a subtraction means for subtracting the difference signal and the internal reference signal to obtain an error. and a filter coefficient calculating means for calculating a filter coefficient by calculating the error signal and setting it in the filter, so that the input video signal falls within the A/D conversion input range.
The gain of the variable gain amplifier is set by the output of the level detection means, and the coefficients of the transversal filter are set based on the output of the level detection means so that the level of the output video signal does not change. A ghost removal device characterized by: