JPS58200674A - Video signal clamping device - Google Patents

Abstract

PURPOSE:To simplify the constitution of a device, by providing a position for clamping a video signal in addition to a horizontal synchronizing signal period including a equivalent pulse period and a pedestal period to perform correctly the clamp of a signal when an interfering signal such as a ghost is mixed. CONSTITUTION:A synchronizing pulse from a input terminal 1 is differentiated and shaped by a differential shaping circuit 6 and made to a reset pulse for the next stage of a counter circuit 7. A pulse C, which is of 8 times a horizontal frequency (fH), is inputted to the circuit 7 from a terminal 8, and a pulse D is outputted with a specified delay behind the synchronizing pulse by FFs 10 and 11 and an ANd circuit 12. The pulse D is supplied to the AND circuit 12 where signals E and F from terminals 13 and 14 are inputted, and the circuit 12 outputs a pulse D'. The pulse D' is supplied to a clamp circuit 20 as a clamp input to set up a clamping position in addition to a horizontal synchronizing signal perido including a equivalent pulse period and a pedestal period, and thus signals which contain interfering signals such as a ghost are correctly clamped.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video signal clamping device that can be used in a system for removing ghosts from television receivers, and is capable of accurately clamping video signals when interference signals such as ghosts are input. It is an object of the present invention to provide a video signal clamping device in which the DC level does not fluctuate due to interference signals.

Although the apparatus of the present invention can be used in all cases of A/D conversion of video signals, a description will be given below using a ghost removal apparatus as an example.

In recent years, when receiving television broadcasts, the deterioration of received images due to various radio wave interferences has become a problem. In particular, the main reason for the rise in buildings in urban areas is double received images.

The so-called ghost phenomenon, which is associated with E-cars, has started to occur frequently. Countermeasures against this problem include the development of wall construction materials that prevent the reflection of radio waves from these buildings, higher directivity of receiving antennas, and diversity reception using horizontally stacked antennas, but all of these methods have operational issues. It has not become widespread due to its complexity and rising costs.

Therefore, there has been an increasing need to provide a fully automatic ghost removal system that can be built into television receivers at low cost.

First, a configuration of a television receiver and a ghost removal device that can perform the misfire 8A will be explained. FIG. 1 shows a part of the configuration of the television receiver. In Figure 1, 1 is an intermediate amplified video detection circuit, which amplifies and amplifies the intermediate frequency modulated signal from the tuner.
Detection is performed to obtain a baseband composite video signal A. This composite video signal A becomes a signal of 0 to 4.2!6 in the NTSC system.

In a normal television receiver, this composite video signal A is directly supplied to both the video signal processing amplifier circuit 3 and the chroma signal processing amplifier circuit 4. The ghost removal device 2 has a function of inputting the composite video signal A, removing the ghost component signal, and then supplying a ghost-free video signal B to the circuits 3 and 4. C shown in the figure is supplied to a video display device (such as a CRT) as a display signal without ghosts.

FIG. 2 is a more detailed block diagram of the portion of the ghost removal device 2 in FIG. 1. A feature of this device is that it uses a transversal filter 6.

As is generally well known, in a television transmitting and receiving system, the transfer function in the radio wave propagation system is H(S), and the transfer function of the propagation system due to ghosts is G(Sl), the transfer function of the total signal propagation system including Tosult and Bostra. is H(S
)・G(s). On the other hand, since the transformer:::'versal filter 5 can have any transfer function,
Ghosts can be removed by controlling to have an inverse transfer function G-' (s) of the propagation system due to ghosts.

The other external part in Fig. 2 is this transversal filter 6.
is the inverse transfer function G−' (S
Ghost detection,operation to automatically control the weighting factor of each tap,so that J.

It performs operations such as generating and storing weighting coefficients. In FIG. V, A is the input composite video signal, B is the ghost-removed output composite video signal, and D is the synchronization signal.

Receiving 1. The detection of a ghost in a television signal that has been
This is done by observing the flatness of the signal after tJ. Ideally, this portion of the signal can be regarded as a step function, and if there is a ghost, distortion of the step function is detected accordingly. For example, the location and size of a ghost is detected at each sampling point. Reference numeral 8 denotes a control tie, and 1: a mink pulse generation circuit, which generates an extraction pulse based on the water and vertical synchronization numbers 1 in order to extract the signal of this part.

The Eishun signal B processed by the transversal filter 6 is added to the clamp A-D converter circuit 7, and after being clamped to eliminate DC fluctuations, the sampled portion is A-D converted by the A-D converter circuit. cost information is obtained, digitized and stored in memory 10.

The circuit 9 processes the cost information stored in the memory 10 and generates a signal for controlling the weighting coefficient when extracting the output signal from each tap of the transformer filter 5. This part is usually configured using a microcomputer.

The weighting coefficient correction circuit 6 is used to actually generate and hold a weighting coefficient for each knob based on the calculation result of the calculation circuit 9. Usually, the output of the calculation circuit 1 Since is a digital signal, if the IJn multiplex coefficient is an analog signal, a D-A conversion circuit is required, and in that case, it is also included.

tfc, such detection → calculation → weighting is repeated (”
Since this is carried out using a so-called adaptive equalization method that is performed once, the weighting coefficients are corrected by 1 many times from one arrow to the next, and it is necessary to store the previous coefficients in the memory 10. The sampling frequency of the A-D converter circuit in the T is required to be three times the band frequency since it handles video signals.
In the SC method, the frequency is 10.3 times the chroma subcarrier frequency.
711III is often used. Therefore, this A-D conversion circuit is required to be high-speed. The memory 10 is also often high-speed, and since a microcomputer is also used as the arithmetic circuit 9, it is not very high-speed, and the memory 10 is used only when the A-D conversion circuit is handling the vertical synchronization signal part. Operation by so-called DMA (memory access) which is disconnected from the microcomputer can be performed.

In this way, this circuit device can be constructed mainly of digital circuits including a microcomputer, and since the transversal filter 5 also has variable integration using a solid-state delay line such as COD, it can be used for TVs at relatively low cost. There are 11 functions to be installed in the John receiver.

Among the ghost removal devices described above, as shown by 7 in FIG. 2, there is a circuit that clamps the video signal, performs A/D conversion, and imports the front and back of the leading edge of the vertical periodic signal into the memory 10 as data. is necessary.

Conventionally, the video signal was clamped using the circuit shown in FIG. Next, this circuit will be explained. In addition, the waveforms of each part of the circuit shown in Fig. 3 are shown in Fig. 4.By inputting No. 111.1 to the base area of the transistor Q in Fig. 3, the waveform shown in Fig. 2B is generated at the collector of the transistor Ql. It is differentiated by the capacitor C1 and the resistor R4 to obtain the pseudo-value shown in Figure 4C, which is shaped, amplified and inverted by transistors Q2 and Q3, and the waveform shown in Figure 4 is obtained from the collector area of the transistor Q3. In this way, if tlB'
The signal shown in is exactly the pedestal partial phase V of the video signal.
Now, this pulse gold 1 is then transistor Q4, capacitor C2, transistor), and the times shown by qs"e.
, :· The signal shown in FIG. 4 applied to the base of transistor Q4 is clamped to obtain the waveform shown in FIG. 4E. This is the so-called pedestal crank circuit.

Currently, the clamp circuit for the ghost removal device uses vertical rotation.

Since data before and after the start of lj is required, v (in this period, 7) is not operating. For this purpose, the third
A signal shown in FIG. 6F is input to terminal T in the figure to prevent clamping of this portion. Figure 6 shows this situation.

Next, we will explain how the ramp operation is performed when a ghost appears in the video signal that is input to this circuit. , Fig. 6 shows an enlarged view of the range of a shown in Fig. 6.) In Fig. 6, A is a signal with no ghost, and B is an image with a normal ghost just at the pedestal. Showing a signal. D indicates a pedestal clamp pulse, and A' corresponds to A, and the video signal clamped by the pulse S is A'.

It is indicated as B' corresponding to BV.

The signal shown in FIG. 6B is a signal containing a normal ghost delayed by the equivalent pulse width (approximately 2.6 μ).

Here, the ghost-free video signal A' is clamped so that the pedestal portion becomes 0. However, the video signal B' with a ghost is also clamped so that the pedestal part becomes 0, but the ghost appears exactly at that position, and the DC component in the pedestal part is originally high, as shown in B'. As shown in Figure 4, the level of the pedestal at the end of the story is much lower.Of course, the level changes depending on the strength of this ghost.

A/D at the 11'' part of the waveform shown in Figure 6 F.
It converts and collects ghost data,
Originally, a signal was input to the A/D converter trison (7) at the very edge of the conversion range in order to make effective use of the converter accuracy (a clamp circuit was required to eliminate the level change). Therefore, based on the signal of Fig. 6 A',
Once the conversion range of the D converter is determined, if the video signal VC contains a ghost at the exact clamping position as shown in FIG. 6B', it will not fall within the A/D conversion range and it will be difficult to obtain accurate data. Here, the position where the ghost enters is random, but at least the ghost is generated when there is a path difference between the two signals, and the ghost will enter the position where the path difference is, so the larger the path difference is, the more the ghost will appear. The more it becomes a ghost, and the slower it becomes a 71 ghost, the smaller the level will be because there will be a difference in path.

From this, the present invention has been made by focusing on the fact that the clamping position is delayed compared to the conventional technique, and even if a ghost appears at that position, the level fluctuation is smaller than in the conventional technique because the level of the ghost 1 is relatively low.

FIG. 7 shows a simple embodiment of the present invention and will be described. Input terminal 1
Inputs either a synchronizing signal or a flyback pulse (FIG. 8B). And this is transistor 2, 3
, a capacitor 4, and a resistor 5, the differential shaping circuit 6 performs differential shaping to generate a reset pulse for the next counter circuit 7. The input of the counter circuit 7 is 8 fH (
A pulse of fH (water/r-frequency) is input from terminal 8, and the frizzofronops 9, 10, 11 . Approximately 69 seconds from the rise of the synchronization signal and flybank pulse by the AND circuit 12
．． The pulse is delayed to a position delayed by 6 μm, and a signal p shown in FIG. 8 is obtained at the output terminal of the AND circuit 12. terminal 13
If we exclude the beginning of the vertical synchronization signal by the signal shown in FIG.
A signal shown in FIG. 8 D' is obtained at the output side of the D circuit 16. This signal is used as the clamp input of a clamp circuit 2o which mainly consists of transistors 16, 18, 19 and condenser 17. The signal of FIG. 8A that is generated can be clamped. This position is the position where the clamp level changes least due to ghosting.

Actually, clamping with this pulse has no problem when A/Ding only the beginning part of the vertical synchronization signal, but when A/Ding the entire video signal, this clamp pulse distorts the video signal part. '1. If this is not the case, input a signal with the waveform shown in FIG. 8F to the terminal 14VC, except for the vertical synchronization signal during the vertical blanking period, and perform clamping during the period in which no video signal is input.

As described above, the present invention is characterized in that the position at which the video signal is clamped is set outside the horizontal synchronizing signal period including the equivalent pulse period and the pedestal period. This allows for accurate signal clamping.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a television receiver with a ghost removal device, FIG. 2 is a block diagram of a ghost removal device, and FIG. 3 is a circuit diagram of a conventional video signal clamp device.
4, 6, and 6 are waveform diagrams for explaining the device,
FIG. 7 is a circuit diagram of a video signal clamping device according to an embodiment of the present invention, and FIG. 8 is a waveform diagram for explaining the device. 6... Differential shaping circuit, 7... Counter circuit, 20... Clamp circuit, 9, 10.11
...Flip-flop, 12.15...
・AND circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person @1
Figure 3 cct

Claims (1)

[Claims] A video signal clamping device characterized in that a position at which a video signal is clamped is set to a position other than a horizontal synchronizing signal period including an equivalent pulse period and a pedestal period.