JPS6386969A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To obtain an ideal ghost eliminating signal by detecting a video signal which can minimize the quantity of a residual ghost, by using a sample rate converter provided with delay adjusting functions for generating plural video signals for equalizing circuit whose sample positions are different. CONSTITUTION:A sample rate converter 104 provided with delay adjusting functions converts to N kinds of equalizing circuit video signals whose delay time of a sample rate is different from each other. Among these converted equalizing circuit video signals, the equalizing circuit video signal of one kind of sample rate is supplied to an equalizing unit 105. As for which signal is used as the equalizing circuit video signal, control is applied so as to minimize residual ghost distortion. In tis way, ghost eliminating signal can be generated as an opposity polarity signal most approximate to an actual ghost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a ghost removal device for removing ghosts from television signals.

(Prior Art) There is a device that uses an equalization circuit to automatically and digitally remove television ghosts. Figure 2 is an example. The details of the operation of this device can be found in the literature (Haka Murakami “Digitalized Ghost Automatic Eraser” Technical Research Report E of Institute of Electronics and Communication Engineers)
MCJ78-37.November 1978).

This device is entirely digitalized, and a digital video signal including ghosts is input to an equalization circuit 2 via an input terminal 1. This equalization circuit 2, as shown in FIG.
N+M unit time delay elements 201 (delay time Tsec
), N1M+1 tap coefficient units 2o2 (digital multipliers), an adder 203 for adding together the outputs of the respective tap coefficient units, and a tap gain memory 204.

The tap coefficients C(-M) to C(N) of this tap coefficient multiplier are set to appropriate values by the control circuit 3, and a digital video signal from which ghosts have been removed is outputted to the output terminal 5.

The basic signal for removing ghosts is the differential waveform of the trailing edge a of the vertical synchronization signal shown in FIG. The peak corresponding to the falling portion of the trailing edge of the signal is set as time base 0, and each peak di after this time base is detected.

di-d(iT)-[-y(t)lt-ITt(i--M-N)... (1) The sign of this differential value old is the positive and negative of the residual ghost with delay time iT. handle. Therefore, the tap gain correction circuit 31 is
Using this differential value old, each tap gain is successively corrected according to the following equation.

Ci, new -Ci, old-△・sgn di(+
--M-N, i≠0)...(2) Here, CI, ol
d is the tap gain before correction, C1゜neW is the tap gain after correction, Δ is a small positive correction coefficient, and equation (2) is expressed as Z
This method is widely known as the ero forcing method.

Note that the center tap coefficient CO is fixed to C0-1 (3). Every time a vertical synchronization signal arrives (176
0 seconds), the ghost is removed by performing this sequential correction.

The sequence controller 4 includes the control circuit 3 described above.
It can be configured using, for example, a ROM. There is also known a device that removes ghosts using a combination of fixed delay circuits and a transversal filter (Japanese Patent Laid-Open No. 158579/1982).

Furthermore, in order to reduce the number of taps in the transversal filter, a method has been proposed in which the video signal input to the transversal filter is delayed by a variable delay circuit in advance, and a ghost is assigned to the transversal filter ( For example, Japanese Patent Application No. 59-273262).

That is, as shown in FIG. 5, the video signal at the input terminal IO is delayed by a variable delay circuit 211 and then supplied to a digital transversal filter 212. The ghost removal signal obtained by the transversal filter 212 (a signal that cancels the ghost, and has a polarity opposite to that of the ghost) is supplied to the adder 213 and synthesized with the video signal from the input terminal 2. be done. If the video signal from the input terminal (2) contains a ghost, this ghost will be canceled by the ghost removal signal. The equalization unit memory 214 is a memory for storing data for controlling the amount of delay of the variable delay circuit 211 and a tap gain given to the multiplier of the transversal filter 212. Furthermore, the latch circuit 215 is for synchronizing the output of the adder 213 with the system clock.

With the above configuration, the interval t1 is captured by the delay amount of the variable delay circuit 211 as shown in FIG. Just take charge. Therefore,
The transversal filter does not need to cover all sections where ghosts may exist (the number of taps can be reduced).

The above example is explained as a device for removing one ghost, but in order to create a system for removing multiple ghosts, as shown in FIG. 6, equalization unit Y1 of FIG.
Equalization units y2 and Y3 similar to the above are prepared, and each equalization unit creates ghost removal signals corresponding to ghosts at different positions (crying phases), and these combined signals are supplied to the adder 220 and input. It may be added to the video signal as a subtraction element. The control circuit 221 is for performing ghost detection and tap gain calculation processing, and supplying the results to each equalization unit.

(Problems to be Solved by the Invention) Recently, television devices that digitally process video signals have been developed, but in this circuit, the sampling frequency is 4 f sc (f sc
: color subcarrier 3.579545M11z) is widely used.

On the other hand, when considering a digital transversal filter, in order to be able to cover a wider range with the same number of taps (see t2 in Figure 4), it is better to operate the transversal filter at a frequency close to the Nyquist frequency. . For this purpose, the applicant placed sample rate converters before and after the equalization circuit to convert the digital data to a lower frequency (8/3fsc), processed it with a transversal filter, and then restored the original data. We propose a system that returns the frequency to the original frequency. In this way, even with the same number of taps, the equalization unit can cover a wider range than when processing a frequency signal with a high sample rate.

For example, when the equalization unit is operated at 4 fsc, 1
28 taps = 128 x 1 / (4f sc) -8,911s
ec range, but when operated at (8/3) f sc, 128 X 1 / ((8/3) f sc)
This means that it can be removed up to a range of -13.4 μsec.

However, when the sampling frequency of the digital video signal is lowered by the sample rate converter, the unit delay time becomes longer. For example, in the case of 4 fsc, it is 0.07 μsec, but in the case of 8/3 fsc, it is 0.1 μsec.

As a result, a new problem arises in that it becomes difficult to accurately align the ghost removal signal with respect to the actual ghost. In other words, in order to cancel the ghost signal as shown in Figure 7, it is necessary to create a cancellation signal with the opposite polarity in the equalization circuit, but the internal signal of the equalization circuit and the sampling position of the digital video signal are Figure 7(a)
, (b), both signals are not symmetrical.

Therefore, even if these are combined, ghosts remain undisappeared ((d) in the same figure). To eliminate this, it is necessary to further increase the number of taps, and the corresponding increase in tap gain and the number of calculations to obtain it also increase.
This will impair the stability of the control system.

Therefore, the present invention has developed a ghost removal method that allows the delay time between taps in the equalization circuit to be finely adjusted, and allows an ideal ghost removal signal to be obtained even if the coverage area is expanded by operating at a frequency close to the Nyquist frequency. The purpose is to provide equipment.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides sample rate converters for converting sample rates at the front and rear stages of an equalization unit having a digital transversal filter. When increasing the ghost coverage range by lowering the sample rate of A video signal that can minimize the amount of residual ghost in the output video signal determined by the phase of each of the plurality of equalization circuit video signals obtained from the regular equalization circuit is detected, and this video signal is passed to the regular equalization circuit. The sample rate converter with delay adjustment function is controlled so that the sample rate converter with a delay adjustment function is adopted as a video signal for use.

(Function) By the above means, the time difference between the ghost delay time and the tap position corresponding to the ghost delay time becomes small, so the transversal filter generates an efficient ghost cancellation signal, and good ghost cancellation is achieved. can get.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which a digital video signal (hereinafter simply referred to as video signal) is supplied to an adder 101 via an input terminal 100, and a sample rate converter 1
It is added with the ghost-removed signal from 06. As a result, a digital video signal from which ghosts have been removed can be obtained at the output terminal 103.

The human video signal is supplied to a sample rate converter 104 with delay adjustment via a switch 102, for example. The switch 102 is a switch that switches the equalization unit between a feedforward type and a feedback type.

The sample rate converter 104 with delay adjustment function converts an input video signal (sample rate 4 f sc) into video signals (of multiple sample rates with different delay times), the specific configuration of which will be explained with reference to FIG. This circuit converts this video signal into an equalization circuit video signal (hereinafter referred to as an equalization circuit video signal). That is, it is converted into N types of video signals for equalization circuits, each having a different sample rate and delay time.

Among the converted equalization circuit video signals, an equalization circuit video signal having one type of sample rate is supplied to the equalization unit 105 .

The equalization unit 105 has the same configuration as shown in FIG. Therefore, in the present invention, the sample rate converter 104 with a delay adjustment function, the delay adjustment control circuit 107 that controls this, the sample rate converter 106 (a circuit for returning the sample rate to the original rate), and their control means. This is different from the previous ghost removal device. Although this embodiment is shown as a system that can eliminate one ghost, more ghosts can be eliminated by adding a system of equalization units, as shown in FIG. 6, for example.

The present invention is characterized by the circuit configuration from the sample rate converter 104 with a one-week delay adjustment function to the sample rate converter 106, which produces a ghost-removed signal, and its control unit. In other words, one equalization unit has a wider range (
If you want to take charge of the interval t2 in FIG. 4 and create a ghost-removed signal for this interval, it is better to lower the drive clock frequency in the equalization unit. However, simply lowering the sample rate using a sample rate converter may result in more residual ghosts or require a larger number of transversal filter taps. explained).

Therefore, in this device, when converting the sample rate, a video signal for the equalization circuit is created with a reciprocal number having a different sample position. This equalizing circuit video signal is, for example, c+c, 9d shown in FIG.

There are three types: 9e.

The sample rate converter with delay adjustment function and the delay adjustment control circuit will be further explained with reference to FIGS. 8 and 9.

FIG. 8 shows a sample rate converter 104 with delay adjustment function.
An example of a specific configuration of the delay adjustment control circuit 107 is shown. A signal at input terminal 300 is supplied to latch circuits 301 to 303 connected in series. These latch circuits 3
01 to 303 operate with a 4fsc clock. The outputs of each of the latch circuits 301 to 303 are input to a selection circuit 304, one of which is selected and supplied to a sample rate converter 305.

Here, the sample rate converter 305 converts the sample rate of input data (4fsc) to a sample rate of 873fsc. The output of this sample rate converter 305 is supplied to series-connected latch circuits 306 and 307. This latch circuit 306.307 is 8/3fs
It is operated by the clock of c. Latch circuit 306.307
The output of is supplied to the selection circuit 308. This selection circuit 308 selects one of the signals based on the control signal from the control circuit 405 and supplies it to the equalization unit at the next stage.

Signal 9a in FIG. 9 indicates the type of sample position (phase), and sample signals A, B, and C of signal 9a are obtained from latch circuits 303 to 301, respectively. Data column 9
b s 9 c is a signal when the delay time is zero. Also, sample signals A and B.

Select one of C and set the sample rate to 8/3fsc
, and converting this back to the original sample rate, the signal 9
As shown in c, 9d, and 9e, the signals are shifted by a time interval of 8 f sc. By simply converting the sample rate, for example, as shown in signal 9e, 1/(81's
c) Only one type of data sequence with a time interval of (see>) can be obtained, but as described above, the sample rate converter 305
By arranging a circuit that combines a latch circuit and a selection circuit before and after the selection circuit, it is possible to obtain a plurality of types of data strings whose sampling positions are shifted according to the selection mode of the selection circuit.

In the figure, each number indicates a sample position, and those with decimal points are data generated by data interpolation. For example, 1.5 is interpolated data of data 1 and data 2.

Therefore, depending on how the control signal is applied from the control circuit 405, the three types of signals 9c and 9d shown in FIG. 9 are generated.

9e can be used as a video signal for the equalization circuit. This data string has a sample rate of 8/3 f sc, but is a signal with different sample positions.

Which signal should be used as the video signal for the equalization circuit can be controlled to minimize residual ghost distortion. For example, sequence processing as shown in Figure 10 is performed to adjust the tap gain. There is a method of employing a signal with the smallest sum of absolute values.

The fact that the tap gain supplied to the coefficient unit of the transversal filter is small means that the tap position matches the ghost delay time accordingly, and it is possible to provide a ghost removal device that reduces the amount of residual ghosts.

The operation up to determining the video signal for the equalization circuit will be described with reference to FIGS. 10, 8, and 1.

First, the vertical synchronization part is taken into the ghost detection circuit 32,
Ghost detection processing is performed. Thereby, each equalization unit 105 is assigned a ghost to eliminate. Next, a process for determining a video signal for the equalization circuit is started (step Sl). First, the sample rate converter with delay adjustment function 104 is controlled by the control circuit 405, and the signal 9C is selected. This signal is used as a video signal for the equalization circuit, and the tap gain of the transversal filter is corrected a predetermined number of times. The tap gain thus obtained is stored in the negative tap gain memory 401 (steps 82 to S4). This memory is provided inside the delay adjustment control circuit 107 in FIG. Next, the tap gain is corrected a predetermined number of times using the signal 9d.

The obtained tap gain is temporarily stored in the tap gain memory 402 (steps 85 to S7). Next, the tap gain is corrected a predetermined number of times using signal 9e. The obtained tap gain is then temporarily stored in the tap gain memory 403 (steps 88 to 510).

Next, the sums of the absolute values of the tap gains of the memories 401 to 403 are compared by the comparator 404, and the smallest of them is determined. Next, the control circuit 405 determines the signal 9c, 9d, or 9e that results in the smallest tap gain field absolute value sum. The signal determined in this way is selected as the video signal for the equalization circuit, and a ghost removed signal is generated.

This allows the ghost removal signal to be created as a reverse polarity signal that most closely approximates an actual ghost. In the above embodiment, one equalization unit was shown as a representative, but
If a plurality of equalization units are connected as shown in FIG. 6, the adopted signal may be determined for each equalization unit so that the ghost of each equalization unit can be effectively canceled.

Generally, when converting the sampling rate from Nl (Hz) to N2 (Hz), a delay time with a frequency interval of the least common multiple of Nl and N2 is realized.

The present invention is not limited to the above-mentioned embodiments, and as shown in FIG. 11, a sample rate converter 104A with a delay adjustment function may be provided at the subsequent stage of the equalization unit 105, and a sample rate converter 106A may be provided at the previous stage. In this case, the sample rate converter 106A lowers the sample rate, and the sample rate converter 104A with delay adjustment function lowers the sample rate.
is set to increase the sample rate.

Another method for selecting a video signal that matches the ghost delay time is to select a video signal that reduces the total amount of residual ghosts after actually performing ghost removal on each video signal. . It is also possible to select the video signal with the maximum tap gain peak, and then synchronously add the input waveforms or output waveforms.
After calculating the ghost delay time, the sample data that best fits the delay time may be selected. In short, the focus of this invention is to match the phase of the video signal to the delay time of the ghost.

[Effects of the Invention] As explained above, according to the present invention, even when the ghost removal signal generating section is operated at a frequency close to the Nyquist frequency, a ghost removal signal with little residual noise can be obtained by finely adjusting the sample position. be able to. Further, the number of taps of the transversal filter to cover one ghost may be smaller, and the sum of absolute values of the tap gains is also smaller, so that control stability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram of a conventional ghost removal device, and FIG. 3 is a block diagram of a conventional ghost removal device.
Figure 4 is a waveform diagram for explaining the ghost removal operation, Figure 5 is a block diagram of the equalization unit, and Figure 6 shows the ghost using the equalization unit in Figure 5. A block diagram of the removal device, Fig. 7 is a waveform diagram to explain the cause of ghost disappearance, and Fig. 8 is a waveform diagram for explaining the cause of ghost removal.
9 is a signal explanatory diagram for explaining the circuit operation of FIG. 8, and FIG. 10 is a flowchart for explaining the operation of the main part of the device of the present invention. FIG. 11 is a circuit diagram showing another embodiment of the invention. 101... Adder, 104... Sample rate converter with delay adjustment function, 105... Equalization unit, 10
6... Sample rate converter, 107... Delay adjustment control circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 5 Control line Figure 7

Claims (1)

[Claims] A sample rate converter for converting the sample rate is provided before and after an equalization unit having a digital transversal filter, and the sample rate inside the equalization unit is lowered to expand the ghost coverage range. In this case, one sample rate converter is a sample rate converter with a delay adjustment function that creates video signals for multiple equalization circuits with different sample positions, and a sample rate converter with a delay adjustment function that creates video signals for multiple equalization circuits obtained from this converter. Among the respective phases, a video signal having a phase as close as possible to the ghost delay time is detected, and the sample rate converter with delay adjustment function is controlled so as to adopt this video signal as a regular equalization circuit video signal. A ghost removal device comprising: means.