JPS6412433B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ghost removal device, and particularly to a ghost removal device that is capable of removing ghosts in a short time when power is turned on or channels are switched.

One example and another example of an apparatus for removing ghosts in a video stage are shown in FIGS. 1 and 2, respectively.
The ghost removal device shown in FIG. 1 uses a transversal filter to realize the ghost transfer function in the video stage after synchronous detection. A video signal including a ghost is supplied to an input terminal indicated by 1 and is supplied to a synthesizer 2.
A cancellation signal simulated by a ghost is supplied from the transversal filter to the synthesizer 2, and a video signal with the ghost canceled is obtained as an output of the synthesizer 2, and is taken out to an output terminal 3. The video signal appearing at the output of this synthesizer 2 is transmitted to the delay circuit 4.
supplied to The delay circuit 4 has a plurality of stages (for example, 256 delay elements) connected in units of sampling periods (for example, 100 [ns]), and n taps are derived from between each stage. The output of each tap of the delay circuit 4 is supplied to a weighting coefficient circuit 5 configured as a multiplier, thereby being multiplied by a weighting coefficient, and all outputs are supplied to an adder 6, and the output of this adder 6 is A cancellation signal is generated.

The weighting factors for the weighting factor circuit 5 described above are generated from an analog accumulator 7. The ghost component is detected by supplying the signal appearing at the output terminal 3 to the detection circuit 8. As a signal for detection and measurement, a signal included in a standard television signal and not affected by other signals for as long as possible, such as a vertical synchronization signal, is used. As shown in Figure 3, based on the waveform obtained by differentiating the leading edge VE of the vertical synchronization signal and the subsequent 1/2H (H is the horizontal section), a weighting coefficient is applied to give proportional weighting. is formed. For example, the delay time τ
If a ghost with a phase difference from the video signal (=ω _c τ, where ω _c is the video carrier angular frequency at the high-frequency stage) of 45° is included, the video waveform as shown in Figure 4A is generated. A signal appears. This signal is differentiated and
By inverting the polarity, a differential waveform shown in FIG. 4B is generated. Since this differential waveform can be approximately regarded as a ghost impulse response, a weighting coefficient proportional to this differential waveform is formed.
Therefore, a differential waveform signal appearing from the detection circuit 8 is supplied to the demultiplexer 9. Similar to the delay circuit 4, the demultiplexer 9 has multiple stages of delay elements connected in units of sampling periods, and n taps are derived from between each stage, and the output of each tap is sent to an analog accumulator. 7.

As mentioned above, the delay circuit 4 and the weighting coefficient circuit 5
By inserting a transversal filter composed of the adder 6 and the adder 6 into the feedback loop, an inverse filter is constructed and ghosts can be removed. In this case, after detecting the waveform distortion in the leading edge of a certain vertical synchronization signal and the subsequent 1/2H interval and determining the weighting coefficient, if any unerased ghosts appear, perform the above-mentioned detection and An analog accumulator 7 is provided to reduce the .

The ghost removal device shown in FIG. 2 is an example in which a ghost is divided into an in-phase component and a quadrature component, the levels of each component are detected, and a cancellation signal is formed by this detection. That is, the output signal of the synthesizer 2 is supplied to a delay circuit 10 having taps, a delayed video signal is extracted from the tap selected by the switching means 11, and this is supplied to the in-phase and quadrature component generation circuit 12. Ru. on the other hand,
The detection circuit 13 detects the in-phase and quadrature components of the ghost from the waveform distortion in the H/2 interval from the leading edge VE of the vertical synchronization signal as shown in FIG. 4A, and each detection output is converted into an analog cumulative signal. Calculator 14I, 1
It will be supplied in 4Q.

The in-phase and quadrature component generation circuit 12 can be formed by using the original signal as it is as the in-phase component.
The orthogonal component can be formed by a transversal filter or a differentiating circuit, and these in-phase and orthogonal components are formed by multipliers 15I and 15, respectively.
Q is supplied. Analog accumulators 14I, 14 as weighting factors for multipliers 15I, 15Q
The output of multipliers 15I and 15Q is supplied to adder 16, and a cancellation signal can be obtained at the output of adder 16.

The ghost removal device shown in FIG. 2 is applied to remove a single ghost, and the switching means 11 is manually switched. The tap of the delay circuit 10 is selected using the switching means 11 while viewing the received image in which a ghost has occurred. The sum of the delay amount determined by the tap selected to minimize the ghost and the time delay generated in the in-phase and quadrature component generating circuit 12 becomes the ghost delay with respect to the desired signal.
Even when removing ghosts by dividing into in-phase components and quadrature components, analog accumulators 14I and 14Q are provided as in the case of FIG.
Through repeated control operations, the number of unerased ghosts is reduced as much as possible.

In the ghost removal device described above, when the reception channel is switched, the weighting coefficient related to the previously received channel is changed to the analog accumulator 7.
Alternatively, it remains held at 14I and 14Q.
This weighting factor is determined by the difference in the video carrier angular frequency ω _c for the new reception channel (this selection is
optionally done by the user),
It is meaningless and may even be the opposite polarity of what is needed to counteract the ghosting of the new incoming channel. Therefore, the time required from switching the reception channel to removing the ghost of the new reception channel becomes significantly longer, or in extreme cases, there is a risk that the ghost removal operation will not converge but diverge.

In view of this point, the present invention is designed to reset the weighting coefficients held to a reference value each time a channel is switched.

Hereinafter, an embodiment in which the present invention is applied to a ghost removal device having the configuration shown in FIG. 1 will be described with reference to FIG. 5. In FIG. 5, 17 is a tuner, 18 is a video intermediate frequency amplifier, and 19 is a synchronous detection type video detection circuit, from which a video signal is applied to the input terminal 1 of the ghost removal device.
The n taps of the delay circuit 4 are supplied to each of the multipliers 21 ₁ -21n of the weighting coefficient circuit via buffer circuits 20 ₁ -20n, respectively. This multiplier 2
A cancellation signal is generated at the output of the adder 6 to which the outputs of 1 ₁ to 21n are supplied.

The analog accumulator has sampling gates 22 ₁ to 2 for n taps of the demultiplexer 9.
2n and capacitors 24 ₁ to 24n are connected via resistors 23 ₁ to 23n. The sampling gates 22 ₁ to 22n provide the leading edge of the vertical synchronization signal to the demultiplexer 9.
It is operated by the sampling pulse from the terminal 25 so that it is turned on for a short time at the timing when the differential waveform in the section after H/2 from VE finishes entering. In this case, a high-level differential waveform corresponding to the leading edge VE of the vertical synchronization signal is not generated from the demultiplexer 9, but n weighting coefficients proportional to the ghost differential waveform are generated from the capacitors 24 ₁ to 24n. and is supplied to multipliers 21 ₁ to 21n.

In this embodiment, n reset switches 26 are connected in parallel to each of the capacitors 24 ₁ to 24n.
Connect ₁ to 26n. This reset switch 2
6 ₁ to 26n are turned on by a reset pulse generated from the OR gate 27. or gate 27
are supplied with the outputs of monostable multivibrators 28 and 29.

The monostable multivibrator 28 is tuner 1
It is triggered by a pulse signal generated at the time of channel switching from 7 to generate a reset pulse of an appropriate pulse width. A normal tuner generates an AFT defect signal to prevent malfunction of the AFT circuit when switching channels, or an audio muting signal to prevent noise when switching channels, so you can use these signals. .

Furthermore, the monostable multivibrator 29 is triggered by the voltage generated at the connection point of both elements of a series circuit of a resistor 31 and a capacitor 32 inserted between the power supply terminal 30 and the ground, and when the power is turned on. A reset pulse of an appropriate pulse width is generated from the monostable multivibrator 29.

As can be understood from the above description of the embodiment of the present invention, at the time of channel switching, the reset switch 26 resets the positive or negative charges corresponding to the weighting coefficients stored in the capacitors 21 ₁ to 21n.
By turning on ₁ to 26n, the discharge is made to zero, so according to the present invention, it is possible to prevent the time required to complete ghost removal of a new reception channel from increasing. Additionally, in the case of electronic channel selection devices, when the power switch is turned off and then turned on again, a predetermined channel is received regardless of the channel that was last received. many. Therefore, if the power is turned on before the charges held in the capacitors 21 ₁ to 21n are discharged, the same problem as when switching channels occurs. Therefore, it is effective to generate a reset pulse even when the power is turned on, as in the above embodiment.

In addition to discharging the charges stored in the capacitors 24 ₁ to 24n and making the weighting coefficient zero, depending on the configuration of the multipliers 21 ₁ to 21n, a predetermined DC voltage may be generated. good. Further, as shown in FIG. 2, the present invention may be applied to a ghost removal device configured to form a cancellation signal by dividing it into an in-phase component and a quadrature component. Furthermore,
The present invention is not limited to the feedback type ghost removal apparatus as shown in FIGS. 1 and 2, but may be applied to a feedback type ghost removal apparatus.

[Brief explanation of drawings]

1 and 2 are block diagrams of one example and another example of a ghost removal device to which the present invention can be applied, and FIG.
4 and 4 are waveform diagrams used to explain the ghost removal device, and FIG. 5 is a connection diagram of an embodiment of the present invention. 1 is the input terminal of the ghost removal device, 3 is the output terminal, 5 is the weighting coefficient circuit, 7, 14I, 14Q
is an analog accumulator, 24 ₁ to 24n are holding capacitors, and 26 ₁ to 26n are reset switches.

Claims (1)

[Claims] 1. In a ghost removal device that simulates a ghost from a video signal to form a cancellation signal, and combines the cancellation signal and the video signal to remove the ghost, weighting for forming the cancellation signal is provided. The memory circuit that holds the count is composed of a plurality of capacitors, and the plurality of capacitors are connected to a common reference potential point at the time of switching reception channels or when switching the reception channel and turning on the power, and the terminal voltage of the plurality of capacitors is 1. A ghost removal device comprising a reset means for resetting the weighting coefficients so that all of the weighting coefficients are equal to a reference value.