JPS6316072B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a television ghost removal device using a transversal filter.

Television ghost removal devices using transversal filters with variable tap gain have recently been actively researched, and some have already been put into practical use at television relay stations and the like.

An example of such a television ghost removal device is shown in FIG. A television signal entering the input terminal IN is introduced into a transversal filter 1. For example, transversal filter 1 is
A delay element 11 with taps made of a charge transfer element such as a CCD, weighting circuits 12 ₁ to 12 _o that multiply each tap output of this delay element 11 by a weighting coefficient (this is called tap gain), and these weighting circuits 12 ₁ ~
12 _o and an adder 13 that adds and synthesizes the output of the input television signal, and by appropriately determining the tap gain, a television signal from which ghost components have been removed can be obtained at the output of the adder 13. ing. This tap gain is given as follows.

Weighting circuit 12 of transversal filter 1
The tap gain to be given to the tap gain memory 5 is stored as digital data in the tap gain memory 5, and the contents of this memory ₅ are read out at an appropriate timing, for example _, during a blanking period, and are then read out to the D/A. After being converted into an analog voltage by a converter 6, it is applied to a tap gain holding circuit 7. The tap gain holding circuit 7 samples and holds voltage values corresponding to each tap gain of the output voltage of the D/A converter 6, and supplies them to the weighting circuits 12 ₁ to 12 _o as tap gains, respectively.

On the other hand, the contents of the tap gain memory 5 are modified as follows. In other words, transversal
The output signal of the filter 1 is led to an output terminal OUT, and is applied to a differentiator 2 to differentiate a certain section in the vicinity of its reference waveform, for example, a vertical synchronization waveform. If there is a ghost component in the output signal of the transversal filter 1, an impulse-like waveform is obtained in the output of the differentiator 2 at the falling part of the vertical synchronization waveform and the ghost component of this falling part. The output of the differentiator 2 is sent to a positive/negative determiner 3 consisting of a level comparator.
The signal is input to the adder 4 via the . The positive/negative determiner 3 determines that the impulse waveform is negative, and at this time the adder 4 adds, for example, -1 to the data in the tap gain memory 5 corresponding to the position (delay time) of this impulse waveform. By repeating this operation, the tap gain of the tap corresponding to the position (delay time) of the ghost component increases sequentially, and the ghost component included in the output of transversal filter 1 decreases accordingly. Then, when the level of this ghost component becomes below the detection limit of the differentiator 2 and the sign/negative determiner 3, each tap gain converges.

By the way, in such a device, once the tap gain converges, if it is left for a long time,
A phenomenon in which the tap gain increases and becomes a divergent state is often observed. Possible causes of this include a timing shift when sampling the error signal, the influence of external noise, and fluctuations in the reference waveform, but such phenomena become more noticeable when the characteristics of the transversal filter are insufficient. This is a major problem when implementing a transversal filter using, for example, a CCD.

In order to prevent this phenomenon from occurring,
A method has been considered in which the tap gain correction operation is stopped after a certain period of time. However, in general, the state of occurrence of ghost components changes over time, and the characteristics of the device itself change over time due to factors such as temperature drift, and it is not possible to respond to these changes if tap gain correction is stopped. The problem arises that it disappears.

This invention was made in view of the above points,
The purpose is to provide a television ghost removal device that can prevent tap gain divergence and at the same time cope with changes in the generation state of ghost components and changes in the characteristics of the device itself over time.

Hereinafter, this invention will be explained in detail with reference to Examples.

FIG. 2 is a block diagram of a television ghost removal device according to an embodiment of the present invention, in which a switch 8 controlled by a timing circuit 9 is inserted between a positive/negative determiner 3 and an adder 4. This is different from Figure 1 in this point.

Here, the timing circuit 9 intermittently generates a series of control pulses as shown in FIG. The output of the adder 4 is supplied to the adder 4. That is, the contents of the tap gain memory 5 are modified only while the switch 8 is closed.

In FIG. 3, the period T ₀ of the first control pulse from the operation start time ts is selected to be a time sufficient for the tap gain to converge, and the periods T ₁ , T ₂ , T of the subsequent control pulses are ₃ ...T _N is a period for correcting the tap gain in response to changes over time in the generation state of ghost components and the characteristics of the device itself, so it is appropriately selected according to these circumstances.

At this time, the total time T = T ₀ + T ₁ + T ₂ +...T _N during which the tap gain is corrected is kept shorter than the time required for the tap gain to increase naturally and reach a divergent state. By doing so, the intended purpose can be achieved.

FIG. 4 shows how the tap gain increases when the tap gain correction amount is 1/512 of the maximum tap gain. Line A shows the case where a ghost with a level of 1 exists, and the tap gain becomes 1 at T _A =8.5 seconds and the ghost is removed. The line B is
This shows that the tap gain increases due to the various causes mentioned above, and even when there is no ghost, it may increase to the maximum value over a long period of time, and experimentally it is estimated that T _B = several minutes to several tens of minutes. The value of is observed.

From this figure, if T ₀ is set to a sufficient time necessary for ghost removal, for example, about 10 seconds, and T ₁ to T _N are set to a time whose sum is sufficiently smaller than T _B , for example, about 1 minute. good.

For example, if T ₁ to _{T N} are each 3 seconds and N = 20, and the correction interval is 12 minutes, the tap gain is corrected for 3 seconds every 12 minutes, and the time until the Nth correction is completed is T. ' is approximately 4 hours.

In this example, the tap gain is no longer corrected after 4 hours have passed, but this poses little practical problem since home television receivers are rarely fixed to the same channel for long periods of time.

Incidentally, if the same channel is to be continuously received for a longer period of time, the contents of the tap gain memory 5 may be cleared once and the above-described series of tap gain correction operations may be repeated again.

As described above, the present invention can simultaneously satisfy two requirements: prevention of tap gain divergence and ability to respond to temporal changes in the generation state of ghost components and temporal changes in the device itself, resulting in improved stability. , good ghost removal effect can be obtained,
It is particularly useful when applied to home television receivers.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a conventional television ghost removal device, FIG. 2 is a configuration diagram of a television ghost removal device according to an embodiment of the present invention, and FIG. 3 is a control pulse used to explain the operation of the same embodiment. FIG. 4 is a diagram showing how the tap gains of the tap corresponding to the ghost component and other taps converge. DESCRIPTION OF SYMBOLS 1... Transversal filter, 2... Differentiator, 3... Positive/negative judge, 4... Adder, 5... Tap gain memory, 8... Switch, 9... Timing circuit.

Claims (1)

[Claims] 1 A transversal filter with variable tap gain to which a television signal is input, a memory for storing the tap gain given to this filter, and a ghost near the reference waveform in the output signal of the transversal filter that stores the contents of this memory. and a device for obtaining a television signal from which ghost components have been removed from the output of the transversal filter, wherein the operation for modifying the contents of the memory is predetermined from the start of operation. A television ghost removal device characterized by comprising a means for temporarily stopping the operation and thereafter repeatedly performing the corrective operation at intervals.