JPS62208763A - Clamp device - Google Patents

Abstract

PURPOSE:To apply clamping at a response speed suitable for the property of a DC level fluctuation of an input signal by increasing the time constant of an LPF so as to slow down the response of the clamping in receiving a satellite broadcast. CONSTITUTION:The LPF 7 consists of a time constant circuit comprising a resistor and a capacitor, and the time constant of the LPF 7 is changed by controlling whether or not a capacitor C2 is connected in parallel with a capacitor C1 by a switch 10. In case the input signal passes through a dispersal elimination and de-emphasis circuit 3, the switch 10 is closed to slow down the time constant of clamp response. In case the input signal does not pass through the said circuit 3, the switch 10 is opened to quicken the time constant of clamp response thereby obtaining a suitable clamp response speed in response to the input signal.

Description

[Detailed Description of the Invention] Industrial Application Field ■ The present invention is MUSI! The present invention relates to a clamp device used in a decoder.

Conventional technology Satellite broadcasting 1 provides high-definition television signals that can obtain higher-definition images than the current standard television broadcasting system.
M performs band compression to enable channel transmission.
The USK method has been proposed.

References: Tasuku Ninomiya et al., [High Definition Television Satellite Single Channel Transmission System (MUSIC) J Television Society Technical Report System Circuit Research Group, TKBS96-2, March 22, 1986, Television Science Technical Report VOL.

7+ /Fil a 4゜This MUSIC signal is transmitted on FM via satellite broadcasting, but in order to improve the S/N of the transmission path and to avoid interfering with the terrestrial communication system, emphasis and dispersal (energy dispersion signal) are applied. is being applied.

Therefore, when the MUSE decoder receives a transmission signal from satellite broadcasting, it performs dispersal removal and de-emphasis, then clamps and A/D conversion for signal processing. The clamp voltage level is M/D
Detect after conversion and LPF.

It is fed back to the clamp circuit through an amplifier. The speed of the clamp response at that time is determined by the time constant of the LPF. In satellite broadcasting, the NC level fluctuates slowly, so a fast response of the clamp is not required, and the response speed of the clamp is slow in order to ensure stability in a weak electric field.

Problems that the invention sought to solve As mentioned above, the MUSIC signal compresses the frequency band of a high-definition television signal to about 1/3, so it is advantageous to record it on a packaged home VTR or video disc. It is. When reproducing these signals with a MUSK decoder, for example, in a VTR, there are DC level fluctuations due to program editing, dropouts, and equipment switching, and a fast clamp response is required. However, as described above, in the clamp circuit of a conventional decoder suitable for satellite broadcasting, the clamp response is insufficient for reproduction of package systems such as the above-mentioned VTR and video disc.

In view of this, an object of the present invention is to provide a clamp device that can obtain a clamp response speed suitable for an input signal.

Means for Solving the Problems The present invention comprises an input circuit that performs dispersal removal and de-emphasis on an input signal, and a first switch that selects either the output signal of this input circuit or another signal. ,
a clamp circuit that clamps the signal selected by the first switch; a DC level detection circuit that detects the DC level of the clamped signal; and a clamp voltage of the clamp circuit that is controlled by integrating the detected DC level. This is a MUSE decoupling clamp device that has an LPF that outputs a signal as a signal, and a second switch that changes the time constant of the LPF, and switches the first switch and the second switch in conjunction.

According to the above-described configuration, the present invention increases the time constant of the LPF and slows down the response of the clamp when a signal passes through the dispersal removal and de-emphasis circuit, that is, when receiving satellite broadcasting. Next, when the signal from the package system is interfaced with a signal that does not pass through the dispersal removal de-emphasis circuit, that is, a signal with flat frequency characteristics, the time constant of the clamp circuit is made small to speed up the response of the clamp.

Embodiment FIG. 1 shows a clamp circuit of a MUSIC decoder in a first embodiment of the present invention.

The satellite broadcast signal is FM demodulated by the BS tuner 1, dispersal removed and de-emphasized, and then sent to the switch 9.
The input end is input to 1,000 people. A signal from the VTR 2 is input to an input terminal B of the switch 9. The signal selected by the switch 9 is clamped by the clamp circuit 4 and converted into a digital signal by the MU/D converter 6. The DC level of the signal clamped by the clamp circuit 4 is A/D converted, detected by the DC level detector, and integrated by the LPF 7.
After being amplified by the amplifier 8, the clamp voltage of the clamp circuit is controlled. The LPFT consists of a time constant circuit of a resistor and a cone capacitor.
The switch 10 controls whether or not 2 are connected in parallel.
Change the time constant of F7. The switches 9 and 10 are interlocked so that when the switch 9 is lying on the person, the switch 10 is on, and when the switch 9 is on the side B, the switch 10 is on. As a specific time constant value, R(01
+Cz) =o+s ~1. o sea , RC1=
o, 1 to Q, 5 See or so is appropriate.

As mentioned above, when the input signal passes through the dispersal removal and de-emphasis circuit, the time constant of the clamp response is slowed down, and when the input signal does not pass through the dispersal removal and de-emphasis circuit, the time constant of the clamp response is made fast. By doing so, it is possible to obtain an appropriate lamp response speed depending on the input signal.

Next, a second embodiment will be described with reference to FIG. 2.

In FIG. 2, the same blocks as those in FIG. 1 are given the same numbers and will be explained. There are cases where the BS tuner 1 is separated from the decoder, and it is unclear whether or not emphasis is applied to the input signal of the decoder. Therefore, a decoder detects whether or not emphasis is applied to the input signal, and determines whether or not to pass the input signal through the dispersal removal and de-emphasis circuit 3. At the same time, set the response speed of the clamp as described above. As a method for detecting whether emphasis is applied to the input signal, attention is paid to the frame pulse added to the MUSIC signal. The frame pulse has the waveform shown in Figure 3 (IL), but when emphasis is applied to this frame pulse, it becomes the waveform shown in Figure 3 (b).
) waveform. Therefore, if the frame pulse has a value of voltage level 5 or higher, it can be detected that the input signal is emphasized.

In FIG. 2, the level person is set by Vraf 14, and the input signal and Vref are compared by comparator 12.

In order to extract only the frame pulse period from the output of the comparator 12, the frame pulse period is detected by the FP detection circuit 16, and the output of the comparator 12 is gated by the gate 13. The output of the gate operates the monomulti 16, and the output controls the time constants of the switch 17 and the LPF 7.

The monomulti 16 operates at a frame period and performs control every frame pulse.

As described above, according to the second embodiment, the response speed of the clamp can be automatically set optimally for the input signal depending on whether emphasis is applied to the input signal.

As described in detail, according to the present invention, even when a MUSE decoder receives a signal from a VTR or satellite broadcasting as an input signal, it can receive a signal from a VTR or satellite broadcasting as an input signal at a response speed suitable for the nature of DC level fluctuation of each human input signal. Clamping can be applied, and the unsightliness of the screen square due to signal DC level fluctuations can be reduced. Moreover, its circuit configuration is simple and its practical effects are very large.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a clamp device according to a first embodiment of the present invention, FIG. 2 is a block diagram of a clamp device according to a second embodiment of the present invention, and FIG. 3 is a waveform diagram of a frame pulse. 3...Dispersal removal de-emphasis circuit, 4...Clamp circuit, 6...A
/ D converter, 6...I) Ctz hell detector,
7...LPF, 8...Amplifier. Name of agent: Patent attorney Toshio Nakao and 1 other person vs.
Figure 1 Figure 3

Claims (2)

[Claims] (1) An input circuit that performs dispersal removal and de-emphasis on an input signal, a first switch that selects either the output signal of this input circuit or another signal, and the signal selected by this first switch. a clamp circuit that clamps the clamped signal, a DC level detection circuit that detects the DC level of the clamped signal, and a low-pass filter that integrates the detected DC level and outputs a signal that controls the clamp voltage of the clamp circuit. and a second switch that changes the time constant of the low-pass filter, and the first switch and the second switch are switched in conjunction with each other. (2) A patent claim characterized in that it has an emphasis detection circuit that detects whether or not emphasis is applied to an input signal, and the first switch and the second switch are controlled by the output of the emphasis detection circuit. The clamping device according to scope 1.