JPH0515571U - Clamp device - Google Patents

Abstract

(57) [Summary] [Purpose] A superimposed signal such as a dispersal signal superimposed on a MUSE signal is stably removed by a feedback clamp. A signal level of a clamp level signal period of an input MUSE signal is averaged by an averaging circuit 12 to obtain an MU.
While the clamp level error is detected by comparing with the specified value that gives the clamp level of the SE signal, the dispersal signal and the power supply hum extracted from the MUSE signal at the HD point of the clamp level error signal and the horizontal synchronization signal and several points before and after it. The integration circuit 14 integrates the difference from the superposed signal such as, and negatively feeds back the integrated output to the input MUSE signal, thereby stably removing the dispersal signal and the like superposed on the MUSE signal by the feedback clamp, Even when the C / N is low, a reproduced image without flicker or horizontal noise can be obtained without being affected by noise.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a clamp device which eliminates a dispersal signal sent superposed on a MUSE signal or a superposed signal such as a power supply hum and enables stable clamping.

[0002]

[Prior Art]

 The MUSE system is a band compression transmission system proposed by NHK as one system for transmitting high-definition signals using the 27 MHz bandwidth of broadcasting satellites, and luminance signals and chrominance signals are multiplexed on the time axis. Specifically, the MUSE signal has the same 1125 scanning lines as HDTV, and one line consists of 480 sampling points with a 16.2MHz sampling clock, and 11 points for the horizontal synchronizing signal and 94 points for the color signal. , 374 points are assigned to the luminance signal. The sync signal consists of a horizontal sync signal whose rising and falling edges are inverted for each line and a frame pulse containing a signal which is inverted every 4 clocks at a 16.2 MHz clock. Therefore, the phase of the resample clock is obtained by controlling the resample error at the midpoint (HD point) to be zero. In addition, a clamp level signal indicating the clamp level of the MUSE signal (128/256 when AD converted to 8 bits) is superimposed on a specific line for each field, that is, the 563th line and the 1125th line, On the receiving side, a clamp level is often calculated in accordance with the AD conversion data of the clamp level signal, and the horizontal synchronizing signal portion is clamped in accordance with the calculated clamp voltage for direct current reproduction.

By the way, in the spectrum of the main carrier of the MUSE signal transmitted from the broadcasting satellite, energy concentrates at a frequency corresponding to a pedestal level or a sync signal level where the time rate of the video signal level is large, and is generated there. Since the peak causes interference when the same frequency is shared with fixed services on the ground, it is specified to reduce the power density of satellite broadcast waves by 22 dB in a bandwidth of 4 kHz. Therefore, in actual satellite broadcasting, a 15 Hz or 30 Hz triangular wave signal synchronized with the frame period of the video signal is superimposed, and the main carrier is shifted by 600 kHz by this signal. The triangular wave signal to be superimposed is called a dispersal (energy diffusion) signal, and its magnitude is 20 mVp-p / 75Ω for a frame pulse of 0.4Vp-p / 75Ω, but the amplitude level is small but This is not possible, and unless the dispersal signal is removed as an unnecessary signal on the receiving side, fluctuations in the luminance level of the reproduced video will result.

In order to remove the dispersal signal, two methods are mainly used: a method of canceling with a triangular wave signal having an opposite phase to this, and a method of clamping the horizontal synchronizing signal described above. Since it is difficult to control the phase and amplitude of signals, the circuits used are complicated, and the manufacturing cost is high due to the large circuit scale. It is often used when processing a dispersal signal that is difficult to remove by the method of clamping the horizontal sync signal because of the large deviation.

On the other hand, a clamp device that removes a dispersal signal with a small frequency deviation by fixing the clamp level to a constant voltage value during the horizontal synchronizing signal period is also called a keyed clamp system and is synchronized with the horizontal synchronizing signal. The horizontal clamp pulse is used as the keying pulse. FIG. 3 shows an example of a conventional keyed clamp type clamping device 1. The input MUSE signal is first amplified by the amplifier 2, then sent to the buffer amplifier 4 via the time constant circuit 3 including the integrating capacitor C and the resistor R, and then supplied to the AD converter 5. A timing signal generation circuit 6 and a clamp level calculation circuit 7 are connected to the AD converter 5, and based on the AD conversion data in the clamp level signal period designated by the clamp signal generation circuit 6, the clamp level calculation circuit 7 calculates the clamp voltage, and supplies the calculated clamp voltage to the time constant circuit 3 via the open / close switch 8 which is closed by the horizontal clamp pulse synchronized with the horizontal synchronizing signal. The time constant circuit 3 is charged by the clamp voltage applied during the clamp level signal period, whereby the clamp operation is performed every horizontal synchronization signal period.

[0006]

[Problems to be solved by the device]

 The above-described conventional clamp device 1 is configured to perform the clamp operation so that the DC level of the video signal is adjusted to the clamp voltage supplied by the clamp level calculation circuit 7 every time the horizontal clamp pulse is input. In order to complete the clamp operation in a short time by using the pulse as the keying signal, the time constant of the time constant circuit 3 including the resistor R and the capacitor C must be shortened. However, if the time constant of the time constant circuit 3 is shortened, when the C / N of the received signal is reduced and a part of the horizontal synchronizing signal is lost due to the influence of the noise component, There was a problem that the clamp level was liable to change because the response operation was quick, and horizontal noise was likely to appear on the playback screen. On the contrary, in order to reduce the horizontal noise caused by the noise component at low C / N, if the time constant of the time constant circuit 3 is increased, the dispersal signal component cannot be sufficiently removed. There was a problem that flicker noise was likely to occur on the playback screen.

[0007]

[Means for Solving the Problems]

 This device is It is a solution to the above problems, A clamp device for direct-current reproducing a MUSE signal on which a superimposed signal such as a dispersal signal for energy diffusion is superimposed. Average the signal level of the clamp level signal period of the input MUSE signal, Clamp level error detecting means for detecting a clamp level error by comparing with a specified value giving a clamp level of the MUSE signal, Superimposition signal extraction means for extracting superimposition signals superimposed on the MUSE signal at the HD point of the horizontal synchronization signal and several points before and after the HD point, An integrating circuit for integrating the difference between the superimposed signal extracted by the superimposed signal extracting means and the clamp level error output, Negative feedback means for negatively feeding back the integrated output of the integrating circuit to the input MUSE signal.

[0008]

The present invention detects the clamp level error by averaging the signal levels of the input MUSE signal during the clamp level signal period and comparing with the specified value that gives the clamp level of the MUSE signal, while detecting the detected clamp level. The difference between the error output and the superimposition signal extracted from the MUSE signal at the HD point of the horizontal sync signal and several points before and after the integration is integrated, and the integrated output is negatively fed back to the MUSE signal to superimpose on the MUSE signal. The superimposed signal such as monkey signal and power supply hum is stably removed by the feedback clamp, and the reproduced image without flicker or horizontal noise is obtained without being affected by noise even at low C / N.

[0009]

【Example】

 An embodiment of the present invention will be described below with reference to FIGS. 1 is a circuit configuration diagram showing an embodiment of the clamp device of the present invention, and FIG. 2 is a signal waveform diagram of each part of the circuit shown in FIG.

The clamp device 11 shown in FIG. 1 averages the signal level of the clamp level signal period of the input MUSE signal in the averaging circuit 12, and detects a clamp level error by comparison with a specified value that gives the clamp level of the MUSE signal. Meanwhile, the integrated circuit 14 integrates the difference between the detected clamp level error output and the dispersal signal extracted from the MUSE signal at the HD point of the horizontal sync signal and several points before and after it, and the obtained integrated output is obtained. The configuration is such that negative feedback is made to the input MUSE signal.

The MUSE signal is first supplied to the non-inverting input terminal of the differential amplifier 15 as the negative feedback means in the first stage, and the difference from the reference voltage given as the feedback input is amplified. The output of the differential amplifier 15 has its unnecessary high-frequency component removed by the low-pass filter circuit 16 and a part thereof is guided to the clamp output terminal, while being supplied to the AD converter 18 via the buffer amplifier 17. The output of the buffer amplifier 17 and the output of the AD converter 18 are respectively taken into the feedback loop via the open / close switches 20 and 21 which are closed by the timing signal generated by the timing signal generation circuit 19.

First, the output of the AD converter 18 is taken into the averaging circuit 12 via the open / close switch 21. However, since the open / close switch 21 is closed in the clamp level signal period, that is, in the period from the 107th point to the 480th point of each of the 563th line and the 1125th line, the averaging circuit 12 calculates the arithmetic average of the clamp level signal of the MUSE signal. To be done. The averaged clamp level signal is supplied to the subsequent subtractor 22, and the difference from the clamp level reference value data (128/256 when AD converted to 8 bits) of the MUSE signal generated on the receiver side is obtained. Be done. The subtractor 22 constitutes clamp level error detection means together with the averaging circuit 12, and the difference output, that is, the clamp level error signal indicating the deviation from the reference value of the averaged clamp level signal, DA conversion is performed in the DA converter 23. The clamp level error signal converted into the analog signal is once held in the holding capacitor C1 and then supplied to the integrating circuit 14 to be used as a reference voltage of the integrating circuit 14.

On the other hand, the output of the buffer amplifier 17 is supplied to the integrating circuit 14 via the open / close switch 20 which is closed by the timing pulse generated by the timing signal generating circuit 19. Since the open / close switch 20 is closed by the clamp pulse designating the HD point of the horizontal synchronizing signal and several points before and after the HD point, the MUSE signal at the HD point is sampled. That is, at the HD point, since only the dispersal signal and the superimposed signal such as the power supply hum are purely superimposed, only such a superimposed signal passes through the open / close switch 20 and is held in the holding capacitor C2. Then, the superimposed signal such as the dispersal signal held in the holding capacitor C2 is supplied to the non-inverting input terminal of the integrating circuit 14. The integrating circuit 14 is a combination of the non-inverting input terminal and the output terminal of the operational amplifier 14a with the feedback capacitor 14c, and the clamp level error signal is supplied to the inverting input terminal. Therefore, the integrating circuit 14 integrates the signal obtained by subtracting the fluctuation amount of the signal level during the clamp level signal period from the dispersal signal or the like superimposed on the HD point. Then, the integrated output of the integrating circuit 14 is returned to the inverting input terminal of the first-stage differential amplifier 15, thereby completing the feedback clamp.

As described above, the clamp device 11 negatively feeds back the signal obtained by subtracting the fluctuation amount of the signal level during the clamp level signal period from the superimposed signal such as the dispersal signal superimposed on the HD point to the input MUSE signal. Even if the clamp level fluctuates, only the superimposed signal such as the dispersal signal at the HD point should be accurately sampled and the sampled dispersal signal, etc. should be removed from the input MUSE signal with the effect of this fluctuation removed. You can Therefore, as shown in FIG. 2 (D), although the influence of the dispersal signal and the like remains slightly before and after the HD point, the influence on the luminance of the reproduced video is visually indistinguishable. Even if a part of the horizontal synchronizing signal or the clamp level signal is lost at low C / N, all the information fed back negatively is smoothed by the integration in the integrating circuit 14, The signal loss does not immediately disturb the clamp operation, which enables high-quality video playback without flicker or horizontal noise.

[0015]

[Effect of the device]

 As described above, the present invention detects the clamp level error by averaging the signal levels of the input MUSE signal during the clamp level signal period and detecting the clamp level error by comparison with the specified value that gives the clamp level of the MUSE signal. The clamp level error signal is integrated with the difference between the HD point of the horizontal sync signal and the dispersal signal extracted from the MUSE signal at several points before and after the horizontal sync signal, and the obtained integrated output is negatively fed back to the input MUSE signal. Therefore, the signal obtained by subtracting the fluctuation of the signal level during the clamp level signal period from the superimposed signal such as the dispersal signal superimposed on the HD point or the power supply hum can be negatively fed back to the input MUSE signal. Even if it fluctuates, the weight of the HD point will be By accurately sampling only the signal and removing the sampled superimposed signal from the input MUSE signal, the influence of the dispersal signal etc. remains slightly before and after the HD point, but it affects the brightness of the reproduced video. The effect is so small that it cannot be visually discerned at all, and even if part of the horizontal sync signal or clamp level signal is lost at low C / N, all the information that is negatively fed back will be in the integrator circuit. Since it is smoothed by integration, the signal dropout does not immediately disturb the clamp operation, which provides an excellent effect such as high-quality video playback without flicker or horizontal pull noise. Play.

[Submission date] August 21, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

On the other hand, the output of the buffer amplifier 17 is supplied to the integrating circuit 14 via the open / close switch 20 which is closed by the timing pulse generated by the timing signal generating circuit 19. Since the open / close switch 20 is closed by a clamp pulse that specifies the HD point of the horizontal synchronizing signal and several points before and after the HD point, the MUSE signal at the HD point is sampled. That is, at the HD point, since only the superposed signal such as the dispersal signal and the power supply hum is superposed, only the superposed signal passes through the open / close switch 20 and is held in the holding capacitor C2. Then, the superimposed signal such as the dispersal signal held in the holding capacitor C2 is supplied to the inverting input terminal of the integrating circuit 14. The integrating circuit 14 is a combination of the inverting input terminal and the output terminal of the operational amplifier 14a with the feedback capacitor 14c, and the clamp level error signal is supplied to the non-inverting input terminal. Therefore, the integrating circuit 14 integrates the signal obtained by subtracting the fluctuation amount of the signal level during the clamp level signal period from the dispersal signal or the like superimposed on the HD point. Then, the integrated output of the integrating circuit 14 is fed back to the reverse input terminal of the differential amplifier 15 in the first stage, thereby completing the feedback clamp.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a clamp device of the present invention.

FIG. 2 is a signal waveform diagram of each part of the circuit shown in FIG.

FIG. 3 is a circuit configuration diagram showing an example of a conventional clamp device.

[Explanation of symbols]

 11 Clamping device 12 Clamp level error detecting means (averaging circuit) 22 Clamp level error detecting means (subtractor) 14 Integrating circuit 15 Negative feedback means (differential amplifier) 20 Superimposed signal extracting means (open / close switch)

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[Procedure amendment]

[Submission date] August 21, 1992

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Claims (1)

[Scope of utility model registration request] 1. A clamp device for direct-current reproducing a MUSE signal on which a superimposed signal such as a dispersal signal for energy diffusion is superimposed, in which a signal level of a clamp level signal period of an input MUSE signal is averaged to clamp the MUSE signal. Clamp level error detection means for detecting a clamp level error by comparison with a specified value giving a level, and superimposition signal extraction for extracting a superimposition signal superimposed on the MUSE signal at the HD point of the horizontal synchronization signal and several points before and after it. Means, an integrating circuit for integrating a difference between the superimposed signal extracted by the superimposed signal extracting means and the clamp level error output, and negative feedback means for negatively feeding back the integrated output of the integrating circuit to the input MUSE signal. A clamping device comprising: