JPH0135545B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a television signal processing circuit used with a ghost removal device for removing ghosts, for example in a video signal stage.

BACKGROUND TECHNOLOGY AND PROBLEMS The following ghost removal device has been proposed. For example, in FIG. 1, a signal from an antenna 1 is supplied to a video detection circuit 4 through a tuner 2 and a video intermediate frequency amplifier 3, and a video signal is detected. This video signal is supplied to a synthesizer 6 via a delay circuit 5 corresponding to the period for eliminating the preceding ghost, and a canceling signal simulating a ghost from a transversal filter, which will be described later, is supplied to the synthesizer 6. A video signal from which ghosts have been removed is output from the synthesizer 6 to an output terminal 7.

Further, the video signal obtained from the video detection circuit 4 is supplied to a delay circuit 8 constituting a transversal filter. This delay circuit 8 has a plurality of stages (n) of delay elements each having a sampling period (for example, 10 [ns]) connected to provide a delay time equal to the preceding ghost removal period.
These taps are derived. Signals from each tap are supplied to weighting circuits 9 ₁ , 9 ₂ . . . 9n each comprising a multiplier.

Furthermore, the signal from the terminal end of the delay circuit 8 is supplied to the terminal 10f of the mode switch 10, and the output signal of the synthesizer 6 is supplied to the terminal 10b of the switch 10. A signal from this switch 10 is supplied to a delay circuit 11. This delay circuit 11 has multiple stages (m pieces) of delay elements each having a sampling period as a unit.
They are connected to have a delay time equal to the post-ghost removal period, and m taps are derived from each stage. The signals from each tap are sent to weighting circuits 12 _{1 and} 12 1 each consisting of a multiplier.
12 ₂ ...is supplied to 12m.

Also, the video signal from the synthesizer 6 is transmitted to the subtracter 13
supplied to Furthermore, the video signal from the delay circuit 5 is supplied to a sync separation circuit 14, and the separated vertical sync signal is supplied to a standard waveform forming circuit 15 and a low-pass filter 16, so that the leading edge VE of the vertical sync signal is
A standard waveform approximating the step waveform is formed. This standard waveform is supplied to the subtraction circuit 13.

The signal from this subtraction circuit 13 is supplied to a differentiation circuit 17 to detect ghosts.

Here, the signal for detecting and measuring ghosts is:
A signal included in the standard television signal and unaffected by other signals for as long as possible, such as a vertical synchronization signal, is used. That is, as shown in FIG. 2, the leading edge VE of the vertical synchronizing signal and ±1/2H before and after it (H is a horizontal period) are not affected by other signals. Therefore, the above-mentioned standard waveform is subtracted from the signal during this period, and the subtracted signal is differentiated to detect the weighting coefficient.

For example, the phase difference ψ with the video signal at delay time τ
(=ωcτ, where ωc is the image carrier angular frequency of the high-frequency stage) If a ghost with a 45° angle is included, the third
A video signal with a waveform as shown in Figure A appears. On the other hand, this signal is differentiated and the polarity is inverted to obtain a ghost detection signal having a differential waveform shown in FIG. 3B, and this differential waveform can be approximately regarded as an impulse response of a ghost.

Then, a differential waveform ghost detection signal appearing from the differentiating circuit 17 is supplied via an amplifier 18 to demultiplexers 19 and 20 connected in series. The demultiplexers 19 and 20 include delay circuits 8,
Similarly to No. 11, delay elements each having a sampling period as a unit are connected in multiple stages, and m and n taps are derived from between each stage. The output of each tap is connected to a switch circuit 21 ₁ ,
21 ₂ ...21n, 22 ₁ , 22 ₂ ...22m.

Further, the vertical synchronization signal from the synchronization separation circuit 14 is supplied to the gate pulse generator 23, and a gate pulse corresponding to the end of the 1/2H section from the leading edge VE of the vertical synchronization signal mentioned above is formed. The switch circuits 21 ₁ to 22m are turned on.

The signals from the switch circuits 21 ₁ to 22m are sent to analog accumulators 24 ₁ , 24 ₂ . . . 24
n, 25 ₁ , 25 ₂ ... are supplied to 25 m. Signals from the analog accumulators 24 ₁ to 25m are supplied to weighting circuits 9 ₁ to 9n and 12 ₁ to 12m, respectively.

These weighting circuits 9 ₁ to 9n, 12 ₁ to 12
The outputs of m are added by an adder circuit 26 to form a cancellation signal. This cancellation signal is then sent to the combiner 6.
supplied to

As described above, the delay circuits 8 and 11, the weighting circuits 9 ₁ to 9n, 12 ₁ to 12m, and the addition circuit 26 constitute a transversal filter, and ghosts are removed. In this case, after detecting the waveform distortion in the leading edge of a certain vertical synchronization signal and the ±1/2H section before and after it and determining the weighting coefficient, if ghosts remain unerased, perform the above-mentioned detection, Analog accumulators 24 ₁ -25m are provided to reduce unerased data.

Note that by switching the mode switch 10, the removal of the rear ghost can be switched to the feedback mode and the feedback mode.

Further, FIG. 4 shows a case where ghosts are removed using an input addition type transversal filter, and parts in the figure that are equivalent to those in FIG.

In the figure, the video signal from the video detection circuit 4 is supplied to weighting circuits 9 ₁ to 9n, and the signals from the weighting circuits 9 ₁ to 9n are respectively supplied to the input terminal of a delay circuit 8'. This delay circuit 8' has n delay elements connected in units of sampling periods, and n input terminals provided between each stage.

Further, the input and output signals of the synthesizer 6 are supplied to terminals 10f' and 10b' of the mode switch 10'. The signal from this switch 10' is supplied to weighting circuits 12 ₁ to 12m, and the signals from these weighting circuits 12 ₁ to 12m are supplied to delay circuit 1, respectively.
1' input terminal. This delay circuit 1
1', m delay elements each having a sampling period as a unit are connected, and m input terminals are provided between each stage.

Signals taken out from the respective terminal ends of these delay circuits 8' and 11' are added by an adder circuit 26' to form a cancellation signal. This cancellation signal is then supplied to the combiner 6.

In this circuit as well, ghosts are removed in the same way as in the circuit using the output addition type transversal filter described above.

Furthermore, it is also possible to obtain a differential output using the difference between the outputs of adjacent bits of the demultiplexers 19 and 20 without providing the differentiating circuit 17 in the above-described circuit, and to perform weighting using this differential output.

Further, the demultiplexers 19 and 20 and the delay circuits 8 and 11 are used in common, and when setting weighting, a weight signal is supplied to the delay circuit, and this is stored in a storage element.
It is also possible to perform weighting using this stored signal thereafter.

In this way, ghosts can be eliminated, for example in the video signal stage.

Furthermore, in such a ghost removal device,
The standard waveform formation and the switching timing of the switch circuits 21 ₁ to 22m use, for example, the leading edge of the vertical synchronization signal as the reference time. In that case, extremely high precision is required to detect this reference time.
Experimentally, it is said that accuracy within 35 nsec is required.

However, in the case of conventional synchronization separation circuits, because the circuit includes a low-pass filter, high-frequency information is lost and the rise of the signal is delayed, making it difficult to derive the reference time from the vertical synchronization signal separated in this way. Detection may cause a time delay.

On the other hand, it has been proposed to form a masking pulse of approximately 1/2H period that includes the leading edge of the vertical synchronizing signal, and to directly detect the leading edge transition using this masking pulse and the video signal.

However, in this method, if the formation position of the masking pulse is incorrect due to the influence of noise or the like, there is a risk that another transition will be detected and the reference time will be significantly deviated. This is particularly a problem since the ghost removal device is often used in conditions where the S/N ratio is poor, such as in the case of a weak electric field.

By the way, since the above-mentioned masking pulse only needs to have a 1/2H period including the leading edge of the vertical synchronization signal, very high precision is not required for forming this masking pulse. Further, since the conventional synchronous separation circuit including a low-pass filter includes the low-pass filter, noise is suppressed, and there is less risk of malfunction due to noise.

Therefore, the inventor of the present application previously proposed the following circuit. In FIG. 5, reference numeral 31 is an input terminal to which a video signal is supplied, and the signal from this terminal 31 is supplied to a sync separation circuit consisting of a comparator 32 and a low-pass filter 33, and the signal from this low-pass filter 33 ( 6A) is supplied to a vertical synchronization separation circuit 34 consisting of a low-pass filter.
The vertical synchronizing signal (FIG. 6B) separated by this separation circuit 34 is supplied to the masking pulse forming circuit 35, and, for example, a triangular wave (FIG. 6C) is formed, and this and the reference potential (broken line) are used to generate the vertical synchronizing signal. A masking pulse (FIG. 6D) corresponding to a 1/2H period including the leading edge of is formed. This masking pulse is applied to the control terminal of comparator 36. Also, the signal from the terminal 31 passes through the amplifier 37 to the comparator 3.
6. For example, by detecting the falling edge of the signal in this comparator 36, the leading edge of the vertical synchronizing signal (FIG. 6E) serving as the reference time is detected, and the t=0 pulse (FIG. 6 F) is taken out to the output terminal 38.

Alternatively, in FIG. 7, the signal from the input terminal 31 passes through a clamping capacitor 41 to a transistor 42 and a resistor 4 that constitute a bias circuit.
3. It is supplied to the connection midpoint between the resistor 43 and the constant current source 44 in the series circuit of the constant current source 44. Further, the signal at the midpoint of this connection is supplied to the base of one transistor 45 constituting the differential amplifier. Further, a resistor 48 and a constant current source 49 of a series circuit including a transistor 47, a resistor 48, and a constant current source 49 forming a bias circuit are connected to the base of the other transistor 46.
Voltage is supplied from the midpoint of the connection. A signal current flowing through the collector of the transistor 45 is extracted through the current mirror circuit 50.

Further, this signal is supplied to a low pass filter 52 and a buffer amplifier 53 through a switch 51, and is also supplied to a low pass filter 55 and a buffer amplifier 56 through a switch 54. The signals from the buffer amplifiers 53 and 56 are connected to the resistor 5.
7 and 58 and supplied to a comparator 59.
A signal from the current mirror circuit 50 is also supplied to a comparator 59.

The signal from comparator 59 is supplied to the clock terminal of D flip-flop circuit 60. Further, the masking pulse from the forming circuit 35 is supplied to the D terminal of the flip-flop circuit 60, and at the same time its polarity is inverted and supplied to the clear terminal of the flip-flop circuit 60.
The output of is taken out to the output terminal 38.

In this circuit, a signal as shown in FIG. 8A, for example, is taken out from the current mirror circuit 50. In response to this signal, switches 51 and 54 are turned on, for example, during the periods shown in FIG. 8B and C, respectively. As a result, potentials E ₁ and E ₂ corresponding to the levels of the synchronizing signal pedestal and sync chip are obtained from the buffer amplifiers 53 and 56, respectively.
These potentials are added by resistors 57 and 58.
Here, if the resistance values of the resistors 57 and 58 are R ₁ and R ₂ , the potential E ₃ obtained by addition is E ₃ =E ₁ R ₂ +E ₂ R ₁ /R ₁ +R ₂ , and R ₂ < If R ₁ , then E ₃ <E ₁ +E ₂ /2. By supplying this potential _E3 to the comparator 59, a signal as shown in FIG. 8D is taken out from the comparator 59. On the other hand, the masking pulse forming circuit 35 outputs a signal as shown in FIG. 8E. By supplying these signals to the flip-flop circuit 60, a signal as shown in FIG. 8F is outputted to the output terminal 38.

In this way, the reference time is detected.

Further, such a ghost removal device is often used in conjunction with, for example, a character multiplexing decoder device. In that case, the decoder device may be provided in the form of an adapter between the tuner device and the monitor receiver, and its configuration is, for example, as shown in FIG. 9.

In the figure, a tuner device 100 includes an antenna 1 to a detection circuit 4, and the received video signal is supplied to a decoder device 200. The video signal supplied in this decoder device 200 is supplied to a ghost removal circuit 201, and a switch 202 selects a signal that has passed through this ghost removal circuit 201 and a signal that has not passed through this ghost removal circuit 201.
The signal from 02 is sent to a character decoder circuit 203 and an encoder circuit 20 for forming a composite video signal.
4 to form a character video signal, this character video signal and the original video signal from switch 202 are selected by switch 205, and the video signal from switch 205 is taken out through amplifier 206. A video signal from this decoder device 200 is supplied to a monitor receiver 300. In this monitor receiver 300, the supplied video signal passes through this signal processing circuit 301 to the picture tube 3.
02, the video signal is also supplied to a synchronization separation circuit 303, and the separated vertical and horizontal synchronization signals are supplied to the deflection yoke of the picture tube 302 through a vertical deflection circuit 304 and a horizontal deflection circuit 305, respectively.

In this way, a character multiplexing decoder device 200 incorporating a ghost removal circuit is formed.

By the way, in the ghost removal device as described above, when the tuner 2 switches the receiving channel, the content of the ghost changes depending on the difference in carrier frequency. Therefore, when switching channels, it is necessary to redo the weighting of the transversal filter.

In that case, until the weighting of the transversal filter converges, a transiently incorrect signal is extracted at the output of the synthesizer 6, and in many cases the image becomes worse than the original signal containing ghosts. I end up. Therefore, when switching channels, it has been proposed that the switch 202 in FIG. 9 be used to directly output the original signal until the weighting is converged.

However, in this case, if switching is performed at arbitrary timing, the DC level and signal amplitude will be different between the output signal from the ghost removal device and the original signal, resulting in accidents such as loss of horizontal synchronization. There is a high possibility that image distortion may occur.

OBJECTS OF THE INVENTION In view of these points, the present invention is intended to prevent image disturbance from occurring when switching between the output signal from the ghost removal device and the original signal.

Summary of the Invention The present invention provides an output via a ghost removal circuit;
The television signal processing circuit is configured to switch between the output signal from the ghost removal device and the original signal at least when switching channels, and to perform the above switching during the vertical blanking period. Image distortion does not occur when switching.

Embodiment In FIG. 10, a signal passing through the ghost removal circuit 201 and a signal not passing through the ghost removal circuit 201 are selected by a switch 202, and are supplied to a receiver 300 through an amplifier 206. Further, a signal indicating that the channel has been switched from the tuner 2 is supplied to the monostable multivibrator 61 to form a negative pulse signal for the time required for the weighting of the transversal filter to converge, and this pulse signal is transmitted to the latch circuit. 62. Furthermore, the video signal is supplied from the detection circuit 4 to the sync separation circuit 14, and the separated vertical blanking pulse is sent to the latch circuit 6.
2 launch terminal. This latch circuit 6
A switch 202 is controlled by a signal from 2.

As a result, a signal that does not pass through the ghost removal circuit 201 is selected for a predetermined period after channel switching, but in this circuit, the latch circuit 6
2 is latched by the vertical blanking pulse, so that if the signal is switched, it will be done during the vertical blanking period, and even if the level fluctuations mentioned above occur, the resulting disturbance will be resolved during the vertical blanking period. There is no risk that the images will be distorted.

Furthermore, FIG. 11 shows an example of a specific circuit. In the figure, a video signal from a detection circuit 4 is supplied to a sync separation circuit 14. Here, the synchronous separation circuit 14 includes a comparator 32 as shown, similar to the circuit shown in FIG.
It may consist of a low-pass filter 33 and a vertical synchronization separation circuit 34, the output of which is also supplied to a masking pulse forming circuit 35. The signal from the synchronous separation circuit 14 is supplied to the latch terminal of the latch circuit 62, and the pulse signal from the monostable multivibrator 61 is supplied to the latch circuit 62. The output of this latch circuit 62 is the switch 20
2, the signal from the ghost removal circuit 201 and the signal from the detection circuit 4 are selected and supplied to the amplifier 206 at the subsequent stage.

In this way, signal selection is performed. In this circuit, latching is performed using a vertical synchronizing signal, but the same effect can be achieved by using a synchronizing pulse, a blanking pulse, a vertical flyback pulse, a masking pulse, or the like. Further, in a device in which the image receiver 300 is integrated, this vertical synchronization pulse can also be supplied to the vertical deflection circuit 304.

By the way, in the above example, the tuner 2 detects when the channel is switched, but with an adapter type device as shown in FIG. 9, it is not possible to obtain a detection signal from the tuner 2 as described above. Therefore, it is necessary to detect the channel switching time from the detected video signal.

FIG. 12 shows a circuit configuration for this purpose. The figure corresponds to the circuit shown in FIG. 5, and the same parts are given the same reference numerals and their explanation will be omitted.

In the figure, the masking pulse from the forming circuit 35 is transmitted to a retrievable monostable multivibrator 71.
is supplied to Here, the masking pulse is formed in synchronization with the vertical synchronization signal, and when the phase of the vertical synchronization signal changes when switching channels, the masking pulse is no longer formed for several vertical periods. Therefore, this masking pulse has a delay time of 1
By supplying the retriggerable monostable multivibrator 71 with a period longer than the vertical period and shorter than the above-mentioned number of vertical periods, an output signal is obtained which inverts only when no masking pulses are formed during channel switching. Note that the masking pulse may not be obtained temporarily due to noise, etc., so the retriggerable monostable multivibrator 71
It is better to set the delay time to two vertical periods or more.

In this way, it is possible to detect the channel switching time from the video signal. Therefore, the output signal of this retriggerable monostable multivibrator 71 can be supplied to the above-mentioned monostable multivibrator 61 to switch the signal.

Although this example has been explained by applying it to the circuit shown in FIG. 5, it can also be applied to the circuit shown in FIG.

It is also possible to reset the weighting of the transversal filter using the detected channel switching signal.

Furthermore, FIG. 13 shows the overall structure of such an adapter. Note that this circuit corresponds to the circuit shown in FIG. 1, and the same parts are given the same reference numerals and the explanation thereof will be omitted.

In the figure, input terminal 2 of a decoder device 200
The video signal supplied to 10 is supplied to delay circuits 5 and 8. Further, the signal from the standard waveform forming circuit 15 is transmitted to the retriggerable monostable multivibrator 7.
is supplied to the first-class channel switching detection circuit 70,
This output signal is supplied to the latch circuit 62, and at the same time, the signal from the sync separation circuit 14 is supplied to the vertical blanking period detection circuit 81, and this detection signal is supplied to the latch circuit 62. The switch 202 is switched by a signal from the latch circuit 62. Note that signals before and after the combiner 6 are supplied to the switch 202.

In this way, the output via the ghost removal circuit and the output without the ghost removal circuit can be switched within the vertical blanking period at least when switching channels.

Although this example has been explained by applying it to the circuit shown in FIG. 1, it can also be applied to the circuit shown in FIG. 4.

Furthermore, by configuring the monostable multivibrator 61 with an RC type time constant circuit in the above-described circuit, it is possible to extract a signal without passing through the ghost removal circuit even during a predetermined period when the power is turned on.

Effects of the Invention According to the present invention, it has become possible to prevent image disturbance from occurring when switching between the output signal from the ghost removal device and the original signal.

[Brief explanation of drawings]

1 to 9 are diagrams for explaining a conventional device, FIG. 10 is a configuration diagram of an example of the present invention, FIG. 11 is a diagram for explaining the same, and FIG. 12 and FIG. FIG. 2 is a diagram for explaining an example. 4 is a video detection circuit, 14 is a synchronous separation circuit, 61
is a monostable multivibrator, 62 is a latch circuit, 201 is a ghost removal circuit, and 202 is a switch.

Claims (1)

[Claims] 1. A switch is provided to select either an output that goes through the ghost removal circuit or an output that does not go through the ghost removal circuit, and at least when switching channels, the switch is controlled to first select the output that does not go through the ghost removal circuit, and the output that does not go through the ghost removal circuit is selected. A television signal processing circuit characterized in that the output via the ghost removal circuit is switched to be selected during the vertical blanking period after the operation of the television signal processing circuit has stabilized.