JPS5860884A - Reference time detecting circuit - Google Patents

Abstract

PURPOSE:To improve the detection precision of reference time by extracting a vertical synchronizing signal from a video signal, converting it into masking pulses and then comparing the pulses with the video signal, and thus directly detecting the transit of the leading edge of the vertical synchronizing signal. CONSTITUTION:A video signal supplied to an input terminal 31 is supplied to the synchronous separating circuit consisting of a comparing circuit 32 and a low- pass filter, and a vertical synchronizing signal component is extracted through the vertical synchronous separating circuit 34. Then, this signal component is supplied to a masking pulse generating circuit 35 to generate masking pulses which correspond to a (1/2)H (horizontal scanning) period including leading edges of the vertical synchronizing signal. Then, the masking pulses and input video signal amplified through an amplifier 37 are supplied to a comparator 36. Thus, when the comparator 36 detects a fall of the signal, the leading edge of the vertical synchronizing signal which corresponds to reference time is detected to appear at an output terminal 38.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for eliminating ghosts in, for example, a video signal stage.
The present invention relates to a reference time detection circuit that is suitable for use in a ghost removal device that uses a ghost removal device.

For example, in FIG. 1, a signal from an antenna (1) is supplied to a video detection circuit (4) K through a chainer (2) and a video intermediate frequency amplifier (3), and a video signal is detected.

This video signal is supplied to a zoom synthesizer (6) via a delay circuit (5) corresponding to the period for eliminating the preceding ghost, and a cancellation signal simulating a ghost from a transversal filter, which will be described later, is sent to the synthesizer (6). (6) k supplied,
From this synthesis (6), a video signal from which ghosts have been removed is taken out to an output terminal (7).

Furthermore, the video signal obtained from the video detection circuit (4) is supplied to a delay circuit (8)k that constitutes a transversal filter. This delay circuit (8) has a sampling period (
For example, a delay element with a unit of 1G (ns) is connected in multiple stages (n pieces) to form a leading ghost removal period and a strong delay time, and n taps are derived from between each stage. It is. The signals from each tap are weighted by multipliers in circuits (91) and (9
2) ... is supplied to (9n).

Further, the signal from the end of the delay circuit (8) is supplied to the mode switch terminal (10f) and also to the combiner (6).
) is supplied to the terminal (fob) K of switch a. The signal from this switch α is supplied to the delay circuit αυ. In this delay circuit, a plurality of stages (m) of delay elements each having a sampling period as a unit are connected to have a delay time equal to the trailing ghost removal period, and m taps are derived from between each stage. It is what was done. The signals from each tap are weighted by multipliers and supplied to circuits (121), (122), . . . -(12m).

The video signal from the synthesizer (6) is also supplied to the subtraction circuit I. Further, the video signal from the delay circuit (5) is supplied to the synchronization separation circuit α4Vc, and the separated vertical synchronization signal is supplied to the standard waveform forming circuit α$ and the low-pass filter aQ to form a step waveform of the leading edge VE of the vertical synchronization signal. An approximate standard waveform is formed. This standard waveform' is the subtraction circuit a3
is supplied to

The signal from this subtraction circuit (I3) is supplied to the differentiation circuit αD to detect ghosts.

As a signal for detection and measurement of small ghosts, a signal that is included in a standard television signal and that is not affected by other signals for as long as possible, such as a vertical synchronization signal, is used. That is, as shown in Figure 2, 5:,i! The leading edge vE of the direct synchronization signal and its front edge are not received. 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 delay time τ causes the phase difference ψ with the video signal (Cτ
, however, ωC is the carrier angle frequency at the high frequency stage) is 45
If a ghost of .degree. is included, a video signal with a waveform as shown in FIG. 3 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, the differential waveform ghost detection signal appearing from the differentiating circuit αη is supplied to the series-connected demultiplexers a through the amplifier a. This demultiplexer a
I, (A) is a circuit in which multiple stages of delay elements each having a sampling period as a unit are connected in the same way as the delay circuit (8) and αυ, and m and n taps are derived from between each stage. be. The output of each tap is a switch circuit (
211), (212)...(21n), (22
s), (22Q)...(22m).

Further, the vertical synchronization signal from the synchronization separation circuit α-hiro is supplied to the gate pulse generator (c), and a gut pulse corresponding to the end of the -H section from the leading edge VE of the vertical synchronization signal mentioned above is formed, and this pulse causes the switch to switch. Circuit (211) ~ (
22m) is turned on.

Signals from these switch circuits (211) to (22ITI) are sent to analog accumulators (241) and (242), respectively.
)...(24n).

(251), (252)...(25m)k are supplied. The signals from the analog accumulators (241) to (25m) are weighted by circuits (91) to (9n), respectively.
(121) to (12an).

These weights are calculated using circuits (91) to (9n), (12
The outputs of t) to (1 mm) are added by an adder circuit 4 to form a cancellation signal. And this canceling signal or synthesizer (
6).

As mentioned above, the delay circuit (8), αυ, and the weighting circuit (9
1) to (9n), (121) to (12m) and the adder circuit (to) constitute a transparsal filter,
-gose) p% removed. In this case, after detecting the leading edge of a certain vertical synchronization signal and the distortion of the waveform in the 10-H section before and after it and determining the weighting coefficient, if ghosts remain unerased, perform the above-mentioned detection, Analog accumulators (241) to (25m) to reduce unerased
is provided.

Note that the trailing ghost removal can be switched to feedforward mode and feedback mode by switching the mode switch K.

Furthermore, FIG. 4 shows a case where one ghost is removed using an input addition type transversal filter, and the same parts in the figure as in FIG.

In the figure, the video signal from the image detection circuit (4) is supplied to the weighted circuits (91) to (9o), and the weighted signals from the circuits (91) to (9n) are supplied to the delay circuits (91) to (9n), respectively. 8'). This delay circuit (8
') is one in which n delay elements each having a sampling 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 connected to the terminal (10f') of the mode switch (10') # (10b'
) K is supplied. The signal from this switch (1G') is supplied to the weighted circuits (121) to (12m)K, and the weighted signals from the circuits (121) to (izm) are input to the delay circuit (11'), respectively. Supplied to the terminal. This delay circuit (11') is a circuit in which 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 a combiner (6)K.

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

Furthermore, without providing the differentiation circuit αη in the above-mentioned circuit,
Demultiplexer 0. It is also possible to obtain a differential output using the difference between the outputs of adjacent bits in (1) and perform weighting using this differential output.

Also the demultiplexer as, an and the delay circuit (8)
, (1m) are set to 1 in common, weighting can be carried out by supplying a weighting signal to the delay circuit at the time of setting, storing this in a storage element, and performing weighting using this storage signal thereafter.

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

By the way, in such a ghost removal device, the timing of the formation of the standard waveform and the switching of the switch circuits (211) to (22m) uses, for example, the leading edge of the vertical synchronization signal as the reference time. In this case, extremely high accuracy is required to detect this reference time.

Experimentally, it is said that accuracy within 35 nllC 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 becomes dull, making it difficult to detect the reference time from the vertical synchronization signal separated by ζθ. This may cause a time delay.

On the other hand, it has been proposed to directly detect the leading edge transit using, for example, a video signal and a masking pulse containing the leading edge of the direct period signal.

However, in this method, if the formation position of the masking pulse is incorrect due to the influence of noise, another transit may be detected and the reference time may be significantly deviated. This is particularly a problem since the ghost removal device is often used in a poor 8/N condition such as in a weak electric field.

In view of these points, the present invention has a simple configuration and is designed to always provide accurate reference time. With reference to the drawings below.

An embodiment of the present invention will be described.

By the way, since the above-mentioned masking pulse only needs to be in the -H period including the leading edge of the 1-period period signal, very high precision is not required for forming this masking pulse. Since a conventional synchronous separation circuit including a low-pass filter includes a low-pass filter, noise is suppressed and there is less risk of malfunction due to noise. The present invention focuses on this point.

In FIG. 5, 01) is an input terminal to which a video signal is supplied, and the signal from this terminal 01) is supplied to a sync separation circuit consisting of a comparator (to) and a low-pass filter (to), and this low-pass The signal from the filter is supplied to a vertical synchronization separation circuit consisting of a q-pass filter. The vertical synchronization signal separated by this separation circuit is supplied to a masking pulse forming circuit to form a masking pulse that occurs during the -H period including the leading edge of the Ii direct synchronization signal. This masking pulse is supplied to the control terminal of the comparator.

Also, the signal from the terminal (goods) is supplied to the comparator (to) through the amplifier (b). When the comparator detects, for example, a falling edge of the signal, it also detects the leading edge of the one-period signal, which is the reference time, and outputs the detection signal to the output terminal.

According to the present invention, the reference time is detected using a masking pulse and a video signal.
Since the transition of the leading edge of the vertical synchronization signal is directly detected, the accuracy is extremely high, and since the masking pulse is formed based on the signal from the one-order period separation circuit including a low-pass filter, this masking pulse There is no risk of formation of any kind due to the influence of noise. Note that in the circuit shown in FIG. 5, the applications for the comparison S03 and the low-pass filter (to) may be reversed.

Furthermore, FIG. 6 shows the circuit of FIG. 5 using specific circuit elements. In the figure, for example, a signal from a transistor (40) in the output stage of a delay circuit is connected through a clamping capacitor (6) to a connection midpoint between a clamping resistor 03 and a constant current source. The signal is taken out to the transistor O?) through a differential amplifier (c) and a current mirror circuit. Therefore, a synchronizing signal as shown in FIG. 7A is taken out to the emitter of this transistor 47).

This synchronization signal is supplied to a low-pass filter consisting of a resistor and four capacitors. Is the signal from this low-pass filter connected to a resistor (to) or a capacitor? It is grounded through 611 and supplied to differential amplifier 63, and positive feedback is applied to differential amplifier υ through current mirror circuit 0 to form an integrating circuit. Therefore, a vertical synchronizing signal as shown in FIG. 7B is output from the current mirror circuit Q.

This vertical synchronization signal is connected to the resistor (b) and capacitor (to).

The signal is fed to a triangular wave forming circuit consisting of transistors.
A signal as shown in FIG. 7C is formed. This signal is supplied to one input terminal of the differential amplifier.

A reference potential as shown in FIG. 7 crtcwt,a is supplied to the other input terminal, and positive feedback is applied to the differential amplifier 6 to form a Schmitt trigger circuit.

The signal from this Schmitt trigger circuit is transmitted through a transistor (
), 61 to the transistor.

Therefore, a masking pulse as shown in Figure 7 is taken out from this transistor.

Furthermore, the signal from the transistor (to) is transferred to the capacitor Iυ
A signal from the transistor 611 is also supplied to the current mirror circuit Q to control the discharge path of the capacitor 611. Here, for example, the time constant of the charging path of the capacitor 6υ is set to be equal to or larger than the time constant 'Ik:l (imllll), and the time constant of the discharging path is set to 30 μm□□.The width of the capacitor 611 widens according to the width of the masking pulse. A small voltage is extracted when the area is narrowed, and a large voltage is extracted when the area is narrowed. When this voltage is supplied to the triangular wave forming circuit, the slope of the triangular wave becomes smaller as the pulse width widens. The time it takes to reach the reference voltage is made longer than k, and the width of the pulse is narrowed, that is, negative feedback is applied to stabilize the formation position of the masking pulse.

A masking pulse is applied to the reset terminal of the BS7 lip-flop circuit, and the video signal from the transistor (40) is applied to the output terminal.
A signal corresponding to the leading edge of the vertical synchronizing signal as shown in ts7 diagram E is outputted to the output terminal -.

In this manner, according to the present invention, it is possible to detect the reference time with extremely high accuracy without fear of malfunction.

[Brief explanation of drawings]

1 to 4 are diagrams for explaining the ghost removal device,
FIG. 5 is a configuration diagram of an example of the present invention, and FIG. 6 is a diagram. FIG. 7 is a diagram for explaining this. 61) is the input terminal, (to), @ is the comparator, (to) is the low noise filter% (goods) is the vertical synchronization separation circuit, 0!9 is the masking pulse forming circuit, (to) is the output terminal .

Claims (1)

[Claims] The video signal is supplied to a sync separation circuit including a low-pass filter, the sync separation output is supplied to a vertical sync signal separation circuit, a predetermined masking pulse including a reference time is formed based on the vertical sync signal, and the masking pulse is A reference time detection circuit configured to detect the reference time using a pulse and the video signal.