JPS6222307B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ghost removal device for a television receiver or the like, and more particularly to a ghost removal device that removes noise from a signal used as a reference signal for ghost detection, such as a vertical synchronization signal, to obtain stable image quality. When receiving television broadcast waves, when reflected waves from obstacles such as high-rise buildings and mountains are superimposed on the direct waves, the so-called double or triple images appear on the screen. Ghost failure occurs. Ghost disturbance has become a major problem in urban areas in recent years, especially with the increase in the number of high-rise buildings, and great efforts are being made in various fields to counter this problem. One possible solution to this problem is to cancel the ghost signal component within the receiver, and various studies and ideas have been made regarding this method. Particularly promising ones include the Proceedings of the 1977 TV Society National Conference and the 1977 Joint Conference of the Four Electrical Engineers of Japan No.
134, there is an automatic ghost removal system that performs waveform equalization of video signals using a transversal filter using a charge-coupled device. In this system, a differential waveform of a vertical synchronization signal is used as a reference signal when performing ghost removal. Figure 1 a shows vertical blanking (vertical retrace period)
Figure b is an example of a waveform near the third line in the figure, in which a delayed signal due to a ghost is added. Diagram c shows the differentiation of this waveform, and if section d in this waveform is detected, information regarding ghosts can be obtained, and the tap gain of the transversal filter is automatically controlled based on this information. By the way, in general, it must be assumed that the video signal received by the receiver includes a considerable amount of noise, and in such a case, the waveforms in diagrams b and c will become b' and c, respectively. 'It will look like the figure. In this way, when the SN is poor, the waveform of the reference signal is disturbed by noise. Jitter occurs in the time reference (timing signal). The automatic ghost removal system is adversely affected by such things, and its operation is significantly hindered. In other words, the disadvantage is that the weighted voltage applied to the transversal filter fluctuates due to noise, causing fluctuations in how the ghost disappears. The adverse effect of this is that the stability of the ghost removal system itself is impaired, resulting in the risk of oscillation. One particular issue is important and will be discussed below. To obtain the system time reference signal, for example, a comparator may be used to detect the midpoint of the falling edge of the third line of the vertical synchronization signal. Due to the presence of noise, jitter occurs as shown in FIG. As a whole system, the clock frequency is
Since a clock of about 10 MHz is used, the period of one clock is about 100 nsec. Therefore, the tolerance of the time reference signal for the system to operate is required to be at most ±50 nsec. Table 1 shows the relationship between the SN ratio of the television signal and the jitter of the obtained time reference signal. According to this, if the SN ratio becomes worse than 30 dB, the jitter of the time reference signal will exceed the operating tolerance of the system, and the system will not operate accurately and the risk of oscillation will increase.

[Table] The present invention was made in view of the above points, and
The present invention provides a ghost removal device that can also prevent malfunctions and oscillations of the ghost removal system due to noise. That is, a reference signal is determined in advance for a signal included in a video signal, the video signal is weighted using a ghost signal of this reference signal as a weighting control signal, and a delay is performed according to the time difference of the ghost signal. When performing ghost removal by extracting a difference signal from a video signal, ghost removal is performed by using the reference signal and a signal obtained by removing noise from the ghost signal as a weighting control signal. Next, an embodiment of the device of the present invention will be described with reference to the drawings. That is, the video signal shown in FIG.
Supply to 2. For example, _the equalization pulse period (E
_P ), the start point of the next vertical synchronization period (V _D ), i.e. the third
The falling period at the end of line (3L) is used. Figure 4b shows an enlarged view of this period, and since the period from the falling point 41 of the third line (3L) to the next rising point 42 is 27.32 μsec, this period covers about half of the screen. Equivalent to. Therefore, since the ghost of half the screen occurs during this period, the configuration of the embodiment of the present invention using the ghost of this period,
Explain the operation. Suppose that a ghost signal (G _H ) as shown in FIG. 4c, for example, is mixed in during this period. In this case, as shown in FIG.
The signal received at 1 is the sum of the signal S ₁ and the ghost signal (G _H ) generated at t ₁ and t ₂ , and this received signal is supplied to the mixer 32 as a positive input. The negative input of mixer 32 is connected to this mixer 3.
The signal obtained from the two outputs via the buffer amplifier 33 is processed by a noise removal circuit 34, a differentiation circuit 35, a weighting control circuit 36, and a transversal filter 40 (consisting of a weighting circuit 37 and a delay circuit 38). This is the resulting pseudo-ghost signal. In the mixer 32, only the signal component _S1 is obtained by subtracting the pseudo ghost signal from the received signal including the ghost signal (G _H ), which is supplied to the television receiver 31 via the buffer amplifier 33. . The buffer amplifier 33 has a gain of, for example, 1,
This output is inputted in parallel to the weighting circuit 37 of the transversal filter 40 constituted by a CCD, and is also inputted to the noise removal circuit 34. In this circuit 34, noise as shown in FIG. 1b' is removed by integral addition, as will be explained later using a circuit example, and its output is supplied to a differentiating circuit 35. The signal differentiated by this circuit 35 is input to a weighting control circuit 36. The output of the weighting control circuit 36 is input in parallel to each of the weighting circuits 37 as a weighting control signal.
Therefore, the output of the weighting circuit 37 controlled by the output of the weighting control circuit 36 is output in parallel.
The signal is input to a delay circuit 38 consisting of a CCD register. The signal input to the delay circuit 38 is read out in series and becomes a pseudo ghost signal. Note that the weighting circuit 37 may be controlled digitally. An example of the configuration of the noise removal circuit 34 in the embodiment of FIG. 3 is shown in FIG. The output of the buffer amplifier 33 in FIG. 3 is input to the color subcarrier generation circuit 12, the synchronous separation circuit 19, and the clamp circuit 23 via the input terminal 10 in FIG. In the color subcarrier generation circuit 12, the color burst signal (C _B ) inserted into the horizontal blanking period (H _P ) of the waveform shown in FIG. 4a is multiplied by 4.
Obtain a clock signal of 4fsc=14MHz. This clock signal is frequency-divided by 1/455 in the frequency divider 11 to obtain a signal of 2f _H =31.5 MHz as shown in FIG. 6a, which is twice the horizontal synchronizing signal. On the other hand, the synchronization separation circuit 19 separates the horizontal synchronization signal and inputs the horizontal synchronization pulse shown in FIG. 6c to the AND circuit 14. The other input of the AND circuit 14 is an inverted version of the signal shown in FIG. 6b output from the frequency divider 11. The signal in Figure 6b is called a wind pulse, and has a width (T _W ) centered around the falling point of 2f _H.
Therefore, the horizontal synchronizing pulse shown in FIG. 6c is ±T _W / centered around the falling point in FIG. 6a.
2, the horizontal synchronizing pulse appears at the output of the AND circuit 14 and resets the frequency divider 11. That is, at this time, the output of the frequency divider 11 is synchronized with the horizontal synchronizing pulse. In this way, the reset of the frequency divider 11 is performed as shown in FIG.
The horizontal synchronizing pulse of deviates from the wind pulse of Fig. 6b,
As a result, the output of the frequency divider 11 is synchronized with the actual horizontal synchronizing signal within the range of the pulse width (T _W ), and therefore the jitter within the pulse width (T _W ) is absorbed. On the other hand, from the frequency divider 11, as shown in FIG. 6d, a time T _A
A pulse train with a width ( _TA ) that rises earlier than a and falls at the falling point of a is also output, and this signal is input to the AND circuit 15. The other input of the AND circuit 15 is connected to a frequency divider 11 as shown in FIG.
This is an output obtained by frequency dividing the output by frequency divider 13 to 1/525, and this signal is a 60 Hz signal equal to the vertical synchronization frequency. Note that the vertical synchronization separation circuit 21 is similar to the synchronization separation circuit 19.
Separate the vertical sync signal from the composite sync signal from
This signal is input to frequency divider 13 as a reset pulse. Therefore, the output of frequency divider 13 is a 60Hz signal synchronized with the actual vertical synchronization signal. Specifically, as shown in FIG. 6f, this signal is a pulse train having a pulse width (T _V ) of approximately H/2 centered at the falling point of the third line during the vertical blanking period. The signal shown in FIG. 6(f) output from the frequency divider 13 is the gate pulse of the AND gate 15, and as long as the pulse train shown in FIG. 6(d) exists within the range of the width (T _V ), the signal shown in FIG. 6(g) The output pulse of the AND gate 15 is input to the waveform averaging circuit 24. This pulse serves as a start pulse for waveform averaging in the circuit 24. As a result, the start pulse shown in FIG. 6g obtained by multiplying and dividing the color subcarrier is precisely synchronized with the color subcarrier, and has a time width of _TW. It is synchronized with the synchronization signal of , and is free of jitter. Therefore, the width of the start pulse (T
If _A ) is set larger than T _W , the required falling portion of the third line portion will be within T _A ±T _W after the rising edge. On the other hand, the noise-containing video signal that enters the input terminal 10 is level-clamped in a clamp circuit 23, and then in a waveform averaging circuit 24, the circuit example of which will be explained later, only the third line of interest is processed every vertical synchronization. The signals are averaged or integrated, and a noise-free signal is obtained at the output terminal 25.
By inputting this output signal to the differentiating circuit 35 in FIG. 3 and differentiating it, the reference signal position can be accurately extracted. Next, an example of the circuit configuration of the waveform averaging circuit 24 in the noise removal circuit 34 of FIG. 5 is shown in FIGS. 7 and 8. The example shown in FIG. 7 is constructed using a parallel circuit, and the example shown in FIG. 8 is constructed using a cyclic circuit. Waveform averaging circuit 2 shown in Figure 7
4 is two N-stage analog shift registers 4.
5, 46 and N integrators 47 provided between each stage of both shift registers. The clamping operation of the clamp circuit 23 and the waveform averaging operation of the waveform averaging circuit 24 start from the rising edge of the start pulse (same as that of FIG. 9a) shown in FIG. 6g. After this point, the falling portion of the vertical synchronizing signal superimposed with noise shown in FIG. 9b is input from the terminal 48. On the other hand, the terminal 49 has a ninth
The sampling clock shown in Figure d is provided,
The vertical synchronizing signal after the rising edge of the start pulse is sampled and sent to the analog shift register 45.
is temporarily held. T is the period of the sampling clock as shown in FIG. 9d. For example, if the sampling frequency is fsc = 14MHz, the period T is
It will be about 70nsec. The values at each stage of the analog shift register 45 are integrated by an integrator 47. Since the above-mentioned portion of the vertical synchronization signal is repeatedly sampled and integrated in the same manner, the influence of noise is removed and the waveform shown in FIG. 9c is taken out from the analog shift register 46, i.e. It is input to the circuit 35. Note that the period of the sampling pulse supplied to the terminal 49 is T, and the analog shift register 45,
Since 46 has N stages, the period during which the signal is clamped and the period during which the signal is sampled in the clamp circuit 23 is NT as shown in FIG. 9c. Offset occurs in parts other than the NT period, but as shown in Figure 9c
Since the signal from which noise has been removed as shown in FIG. Differential pulses caused by a level difference at the boundary with the NT period are removed after passing through the differentiating circuit 35, for example. In the circuit example of the waveform averaging circuit 24 shown in FIG. 8, one N-stage analog shift register 51 is used, and the output thereof is appropriately attenuated by an attenuator 52 and added to the input signal by an adder 53. The configuration is such that the input signal is held in the analog shift register 51 again. In this configuration, the terminal 54 receives the falling portion of the vertical synchronizing signal superimposed with noise as shown in FIG. 9b, and the terminal 55 receives the sampling pulse. In this case as well, the sampling start point is the rising edge of the start pulse shown in FIG. 6g (FIG. 9a). In this case, the sampling values are accumulated by feedback, and the vertical synchronizing signal shown in FIG. 9c is obtained at the output terminal 56 by averaging and suppressing noise. Note that if the signal input to the terminal 32 is passed through the time axis expansion circuit in advance, it is possible to reduce distortion of the signal waveform, and furthermore, there is an effect that it is easier to form the weighted control signal. As mentioned above, T in FIG. 9 represents the sampling period, and NT represents the length of the section in which waveform averaging is performed. It is well known that noise can be removed by adding and averaging waveforms using these integration effects, but in the present invention, the particularly stable divided output of the color subcarrier is used as the time origin when performing integration. By increasing the time constant of the integral effect, a very stable and jitter-free output waveform can be obtained. The improvement rate in the example shown in Figure 8 is √
For example, if n=100, the SN ratio is
Improved by 20dB. As can be seen from Table 1, the improvement rate of 20 dB is almost sufficient for practical use. By the way, in the embodiment of the present invention shown in FIG. 3, the noise removal circuit 34 is not necessarily placed at the position shown in the figure, but is placed after the differentiation circuit 35, and performs waveform averaging (integration) on the differentiated vertical synchronization signal. You may also do so. Further, in the above embodiment, the case where integration is performed in an analog manner has been described, but it goes without saying that integration may be performed digitally. In the present invention, by changing the position of the start pulse or the length of the waveform averaging section, not only the falling part of the third line but also the equalization pulse in vertical blanking, color burst, VIR, The same noise removal effect can be achieved with respect to VIT and reference signals inserted for some purpose. At this time, if it is desired to operate only on odd or even fields, it is sufficient to determine whether the field is odd or even with respect to the synchronization signal and control the generation of the start pulse accordingly. As described above, according to the present invention, the waveform of the target portion of the vertical synchronization signal is sufficiently noise-removed, and the risk of noise-induced ghost removal fluctuations, malfunctions, and oscillations in the automatic ghost removal system is sufficiently eliminated. be able to.

[Brief explanation of the drawing]

Figure 1 is a diagram of the vertical synchronization signal and its differential waveform when ghost and noise are added to explain the operation of a conventional ghost removal device, and Figure 2 shows automatic ghost removal using the noisy signal shown in Figure 1. FIG. 3 is a block diagram for explaining an embodiment of the device of the present invention.
4a, b, and c are pulse waveform diagrams for explaining the operation of FIG. 3; FIG. 5 is a block diagram for explaining a specific example of the noise removal circuit in FIG. 4;
6 is a pulse waveform diagram for explaining the operation of FIG. 5, FIGS. 7 and 8 are circuit configuration diagrams showing a specific example of the waveform averaging circuit of FIG. 5, and FIG. 9 is a diagram of the waveform averaging circuit of FIG. 9 is a pulse waveform diagram for explaining the operation of FIG. 8. FIG. 31... Television receiver, 32... Mixer, 34... Noise removal circuit, 35... Differential circuit, 36... Weighting control circuit, 37... Weighting circuit, 38... Delay circuit, 40... Transversal filter.

Claims (1)

[Scope of Claims] 1. After weighting the video signal by forming a weighting control signal from a ghost signal of a predetermined reference signal included in the video signal and delaying the ghost signal according to the time difference between the ghost signals, A ghost removal device characterized in that when performing ghost removal by extracting a difference signal from a video signal, a signal obtained by removing noise from the reference signal and the ghost signal is used as the weighting control signal. 2. The ghost removal device according to claim 1, wherein the falling portion of the third line in the vertical retrace period is used as the reference signal. 3. Ghost removal according to claim 1, wherein the noise removal circuit divides the color burst signal and integrates the clamped video signal using a start pulse synchronized with a synchronization signal in the video signal. Device.