JPS60160269A - Waveform equalizing circuit - Google Patents

Abstract

PURPOSE:To form excellent waveform equalization with simple constitution by detecting a SYNC tip level and a pedestal level of an input video signal and making the detected values coincident with the amplitude of a reference waveform. CONSTITUTION:When a signal of vertical synchronism period applied with SYNC tip clamp as shown in Fig. A is inputted to an input terminal 31 of a reference waveform forming circuit 14, a pulse B is outputted from a masking pulse forming circuit 35 and the pedestal level of the input signal is sampled and held by a sample-and-hold circuit 48 via a sampling pulse generating circuit 49. A t=0 pulse D is outputted from a comparator 36 and a signal E delayed by a monostable multivibrator 38 is formed. The level of the signal E is limited by a limiter circuit 47 so that its low voltage part is a clamp potential Ec from a clamp potential generating circuit 46 and a high potential potential part is a hold potential Es from the circuit 48, a signal F having the amplitude from the STNC tip level Ec of the input signal to the pedestal level Es is outputted and a reference waveform G is formed via an LPF40.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a waveform equalization circuit that performs waveform processing of, for example, a video signal.

BACKGROUND ART AND PROBLEMS The following ghost removal device has been proposed as an example of a waveform equalization circuit. 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 sent to a synthesizer (6) via a delay circuit (5) corresponding to the period for eliminating the preceding ghost.
At the same time, a cancellation signal simulating a ghost from a transversal filter (described later) is sent to this synthesizer (
6), and from this synthesizer (6) the deghosted video signal is supplied to a switch (7). Further, the video signal from the video detection circuit (4) without ghost removal is supplied to a switch (7), and the signal from this switch (7) is taken out to an output terminal (71).

Further, a 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 sampling period (
For example, a plurality of delay elements yIt (n) each having a unit of 10 (ns) are connected to provide a delay time equal to the preceding ghost removal period, and n taps are derived from between each stage. . The weighting circuits (9z) and (9z) are used to weight the signals from each tap using multipliers, respectively.
92) ... is supplied to (9n).

Furthermore, the signal from the end of the delay circuit (8) is supplied to the terminal (10f) of the mode switch αΦ, and the signal from the end of the delay circuit (8) is supplied to the terminal (10f) of the mode switch αΦ.
) is supplied to the terminal (10b) of the switch aω. The signal from this switch (10) is transmitted to the delay circuit (1
1). In this delay circuit (11), a plurality of stages (m) of delay elements each having a sampling period as a unit are connected to provide a delay time equal to the post-ghost removal period, and m delay knobs are connected between each stage. It has been derived. Weighting circuits (121), (122), etc. (121), (122)... (
12m).

Also, the video signal from the synthesizer (6) is sent to the subtraction circuit (13).
supplied to Furthermore, the video signal from the video detection circuit (4) is supplied to a reference waveform forming circuit (14) to form a reference waveform that approximates the step waveform of the leading edge VE of the vertical synchronization signal. This reference waveform is supplied to a subtraction circuit (13).

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

Here, as a signal for detecting and measuring ghosts, a signal that is included in a standard television signal and is not affected by a signal that lasts 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 the distance +H 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 of this period, and this subtracted signal is differentiated to detect the weighting coefficient.

For example, the phase difference with the video signal ψ (=ωCτ
, however, ωC is the image carrier angular frequency at the quotient frequency stage) is 45
If a ghost of " is included, a video signal with a waveform as shown in FIG. 3A appears.

On the other hand, by differentiating this No. 14 and inverting the polarity, a ghost detection signal with a differential waveform similar to that shown in Figure B of wS3 is obtained, and this differential waveform can be approximately regarded as the 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 a demultiplexer (19) connected in series. These demultiplexers (19) and (20) are delay circuits +
81. Similar to (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 the switch circuit (21z), (2
12) ...(21n), (221), (222
) ... is supplied to (22m).

Further, the vertical synchronization signal extracted by the reference waveform format circuit (14) is supplied to the gate pulse generator (23), and a gate pulse corresponding to the end of the +I (section) is formed from the leading edge VE of the vertical synchronization signal mentioned above. This pulse turns on the switch circuits (2k) to (22m).

Signals from these switch circuits (211) to (22m) are sent to analog accumulators (241) and (242), respectively.
・ (24n), (25z), (252)...
(25m). This analog accumulator (24
The signals from 1) to (25m) are weighted by the circuit (
91) to (9n), (12t) to (12m).

These weights are applied to circuits (91) to (9n), (121)
The outputs of (12n) are added by an adder circuit (26) to form a cancellation signal. This cancellation signal is then supplied to the combiner (6).

As mentioned above, a transversal filter is configured by the delay circuit [81, (11), weighting circuits (91) to (9n), (121) to (12m), and addition circuit (26), and ghosts are removed. be done. In this case, after detecting the distortion of the waveform in the leading edge of a certain vertical synchronization signal and the +H section before and after it and determining the weighting coefficient, if ghosts remain unerased, perform the above-mentioned detection and Analog accumulators (241) to (25I1
1) is provided.

Note that by switching the mode switch Qψ, the rear ghost removal can be switched between the feedforward mode and the feedback mode.

Furthermore, Fig. 4 shows the case where ghosts are removed using an input addition type transversal filter.
Portions equivalent to those in the figures are given the same reference numerals and detailed explanations will be omitted.

In the figure, the video signal stage weighting from the video detection circuit (4) is supplied to the circuits (91) to (9n), and the weighting means that the signals from the circuits (91) to (9n) are respectively supplied to the delay circuits (8). ') is supplied to the input terminal. This delay time 11 (
8') is one in which n delay elements each having a sampling link period as a unit are connected, and n input terminals are provided between each stage.

Also, the signals on the input side and output side of the synthesizer (6) are the terminals (10f') + (10b) of the mode switch (10').
') is supplied. The weighted signals from this switch (10') are supplied to the weighted circuits (121) to (12m), and the weighted signals from the weighted circuits (12z) to (12m) are respectively input to the delay circuit (11'). Supplied to the terminal.

This delay circuit (11') has m delay elements connected in units of sampling periods, and m input terminals provided between each stage.

Signals taken out from the respective terminal ends of these delay circuits (8') + (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-mentioned circuit, and to perform weighting using this differential output. can.

In addition, the demultiplexers (19) and (20) and the delay circuits (81 and (11)) are used in common, and for weighting, a weight signal is supplied to the delay circuit at the time of setting, this is stored in the memory element, and the stored signal is used thereafter. It is also possible to perform weighting based on

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

By the way, in such a ghost removal device, the formation of a reference waveform has conventionally been performed as follows.

In FIG. 5, (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). , the signal from this low-pass filter (33) (FIG. 6A) is supplied to a vertical synchronization separation circuit (34) consisting of a low-pass filter. This separation circuit (
The vertical synchronization signal (Fig. 6B) separated by 34) is supplied to the masking pulse forming circuit (35), and a triangular wave (Fig. 6C), for example, is formed. A masking pulse (FIG. 6D) corresponding to the +H period including the leading edge of is formed. This masking pulse is applied to the control terminal of the comparator (36). Further, a signal from the terminal (31) is supplied to the comparator (36) through the amplifier (37). By detecting, for example, a falling edge of the signal in this comparator (36), the leading edge of the vertical synchronizing signal (FIG. 6E), which serves as the reference time, is detected. This signal is supplied to the monostable multipipe lake (38) corresponding to the delay circuit (5) and becomes the reference time t.
=Q pulse (FIG. 6F) is formed. This t=Q pulse is applied to the gain control amplifier (39) and the low-pass filter (40).
), the amplitude is adjusted and the waveform is adjusted to form a reference waveform, and the reference waveform is taken out to the output terminal (41).

Here, the amplitude of the reference waveform is set in a standard tuner device. The gain control amplifier (39) is configured for this purpose.

However, generally the video signal from the tuner device is
It is not necessarily in a standard state due to variations in the characteristics of the detection circuit, etc., and the influence of electric field strength. Therefore, there is a possibility that the amplitude of the synchronizing signal will be larger or smaller than the standard lVppX-4.

On the other hand, in a ghost removal device, when a vertical synchronization signal with a size different from the reference waveform is input, it is assumed that a ghost with a delay time of 0 has been superimposed, and the waveform is equalized (
AGC operation). For this reason, the output terminal of the ghost removal device (
71), a signal is extracted in which the level of the video signal is changed in proportion to the amplitude of the synchronizing signal becoming the standard level.

However, in this case, the device generally uses the switch (7) to extract the video signal from which the ghost has not been removed until the ghost removal has converged, and then automatically switches the switch (7) after the ghost removal has converged. As mentioned above, when the level of the video signal changes, the brightness of the screen changes. Therefore, if the brightness of the television receiver is set to the optimum value before switching, the brightness will change after switching,
You will have to make adjustments again.

Further, a part of the waveform equalization capability is used for the above-mentioned AGC operation, and the original ghost removal capability is reduced.

That is, when a standard video signal is input manually, as in the case of No. 7111A, for example, an output having the same shape as that without ghosting is obtained. When the level of the input video signal is low as shown in FIG. 7B, the output becomes larger than the input. Further, when the level of the input video signal is high as shown in FIG. 7C, the output becomes smaller than the input. Furthermore, if the human synchronization signal is shrunk as shown in Figure 7 due to distortion in the detection circuit, the output video level will become excessive. Also the 7th
If the input synchronization signal is extended as shown in Figure E, the output video level will be too low.

In this way, the level of the video signal is changed, and this A
Part of the waveform equalization capacity is used for GC operation.

On the other hand, for general users, gain control amplifier (39)
It is difficult to make adjustments, and there is an extremely high risk of accidents due to incorrect adjustment.

OBJECTS OF THE INVENTION In view of these points, the present invention is intended to perform good waveform equalization with a simple configuration.

Summary of the Invention The present invention uses a vertical synchronization signal of an input video signal as a reference signal for waveform equalization, uses an ideal vertical synchronization signal as the original waveform as a reference waveform, amplifies the difference between the two, and uses a transversal filter. In a waveform equalization circuit that reduces waveform distortion by giving it as a tap weight, the sync tip level and pedestal level of the human video signal are detected, and the amplitude of the reference waveform is made to match these detected values. This waveform equalization circuit is characterized by the following: According to the waveform equalization circuit, excellent waveform equalization can be performed with a simple configuration of m.

In Fig. 8 of the embodiment, °C1 is generally used at the input terminal of the waveform equalization circuit.
A clamp circuit (42) such as a sync tip clamp is provided to regulate the potential of the high power video signal. In other words, the video signal from the video detection circuit (4) is connected to the capacitor (43).
) to the buffer circuit (44), and the connection midpoint between this capacitor (43) and the buffer circuit 1m (44) is connected to the power supply terminal Vcc via a transistor (45). And at the base of the transistor (45),
The clamp potential generation circuit (46) generates a desired clamp potential Ec + Vig (
Vw is supplied with the base-emitter voltage of the transistor. This performs sync tip clamping.

Then, the output signal of the buffer circuit * (44) is transferred to the delay circuit (5
) etc.

The signal from this clamp circuit (42) is also supplied to the human power terminal (31) of the reference waveform forming circuit (14).

In this reference waveform forming circuit (14), the circuits up to the monostable multi-bi break (38) are constructed in the same manner as in the conventional circuit. Furthermore, the output signal of the multivibrator (38) is supplied to the limiter circuit (47). This limiter circuit (47) generates a clamp potential I! A clamp potential Ec from &(46) is supplied.

Also, a signal from the input terminal (31) is supplied to the sample bold circuit (48). Furthermore, the signal from the masking pulse forming circuit (35) is supplied to the sampling pulse generating circuit (49), which generates a pulse immediately after the leading edge of the masking pulse, and this pulse is supplied to the sample and hold circuit (48). Ru.

This sampled and bolded potential Es is then supplied to the limiter circuit (5o).

Here, for example, when a vertical synchronization period with sync chip clamping as shown in FIG. 9A is input manually to the terminal (31), the masking pulse forming circuit (35) outputs a vertical synchronization period as shown in FIG. 9B.
A masking pulse as shown in is output. When this masking pulse is input to the sampling pulse generation circuit (49), a sample bold pulse similar to that shown in FIG. 9C is generated from this circuit. As a result, the pedestal level of the human video signal is sampled and held in the sample and hold circuit (48).

On the other hand, from the comparator (36), t=Q as shown in Figure 9.
A pulse is output and this signal is supplied to a monostable multivibrator (38) to form a signal delayed by a predetermined time as shown in FIG. 9E.

Note that the output of the multi-by-break (38) is made to have an amplitude sufficiently larger than the level limited by a limiter circuit (47), which will be described later.

A signal from this multi-by-break (38) is supplied to a limiter circuit (47). And this limiter circuit (
47) Restriction is performed so that the low potential portion becomes the clamp potential EC1 from the clamp potential generation circuit (46) and the high potential portion becomes the hold potential E3 from the sample and hold circuit (48). This allows the limiter circuit (5
0) outputs a signal with an amplitude ranging from the sync tip level Ec of the input video signal to the pedestal level Es, as shown in FIG. 9F. This signal is further supplied to a low pass filter (40) to form a reference waveform that approximates the desired step waveform as shown in FIG. 9G.

Waveform equalization is performed using this reference waveform. In the above explanation, only the main circuits were shown, but the other parts are the same as those in FIGS. 1 and 4.

Waveform equalization is performed in this way, but according to this circuit, the amplitude of the reference waveform is matched to the amplitude of the synchronization signal of the input video signal, so no AGC operation is performed, and the input and output are The video signal level never changes. In other words, the level is equal to the input, and an output signal with only ghost removed is obtained.

Therefore, even if switching is performed after ghost removal has converged, the brightness will not change, and a part of the waveform equalization capability will not be used by the AGC operation. Note that the level correction is performed by an AGC circuit or the like of the television receiver.

Further, in the above-described circuit, the limiter circuit (47) is specifically constructed as shown in FIG. In the figure, an npn transistor (52) is provided between the signal line (5) and the power supply terminal Vcc, and the clamp potential Ec+VB1 from the clamp potential generation circuit (46) is supplied to the base of this transistor (52). Ru.

Also, the potential Es from the sample hold circuit (48) is n
A predetermined type (qVm) is supplied from a voltage dividing circuit (55) to the base of an NPN transistor (54) whose collector and emitter are commonly connected to this transistor (53). Furthermore, a pnp transistor (56) is provided between the signal line (51) and ground, and the base of this transistor (56) is supplied with the potential from the emitters of the transistors (53) and (54).

Furthermore, between the signal line (51) and ground I)nl))
A transistor (57) is provided, and this transistor (57) is provided.
7) from the voltage divider circuit (58) to the base of
Veε is supplied.

In this circuit, the low potential part of the signal is connected to a transistor (
52) The clamp potential (sync chimp level) E
c.

In addition, the higher of the hold potential (pedestal level) Es and the potential Vm is taken out by the transistor (53) <54), and the high potential part of the signal is limited to this higher potential by the transistor (56). , transistor (
57), this potential is prevented from becoming higher than the potential V1.

Therefore, in this circuit, the low potential part of the reference waveform is limited to the sync tip level, the high potential part is limited to the pedestal level, and furthermore, this high potential part is within a predetermined range across the reference 1VppX□. (VI11 to ■l) so as not to become too large or too small. In other words, the high potential part is the first
As shown in Figure 1, Vm-V7! In the range of Vs = VJ
and beyond that, Vs = Vm or Vs = V
It is assumed that the Vi-Vs characteristic is β.

As a result, when the amplitude of the synchronization signal is too large or too small, the AGC operation is performed to perform more stable waveform equalization.

Effects of the Invention According to the present invention, it has become possible to perform good waveform equalization with a simple configuration.

[Brief explanation of drawings]

1 to 7 are diagrams for explaining a conventional device, FIG. 8 is a configuration diagram of an example of the present invention, and FIGS. 9 to 11 are diagrams for explaining the same. (14) is a reference waveform forming circuit, (46) is a clamp potential generation circuit, (47) is a limiter circuit, and (48) is a sample bold circuit. Fig. 7 input/output 11~],

Claims (1)

[Claims] By using the vertical synchronization signal of the input video signal as a reference signal for waveform equalization, using the ideal vertical synchronization signal as the original waveform as the reference waveform, and amplifying the difference between the two and giving it as the tap weight of the transversal filter. A waveform equalization circuit for reducing waveform distortion, wherein a sync tip level and a pedestal level of the human video signal are detected, and the amplitude of the reference waveform is made to match these detected values. circuit.