JPH0438194B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a color signal processing circuit, and in particular to a color signal processing circuit for removing amplitude noise of color signals in video tape recorders (VTRs), color television receivers, etc. Related to signal processing circuits.

[Prior Art] The prior art will be explained using a home VCR as an example. In a home VTR, a composite video signal is separated into a luminance signal component and a color signal component, and the luminance signal component is converted to a low carrier FM signal, and the color signal is converted to a low frequency (for example, 629kHz in the case of VHS NTSC system). The components are superimposed and recorded on tape. During playback, the head amplifier output is separated by a filter into a low carrier wave FM signal and a low frequency converted color signal, and a luminance signal component obtained by demodulating the low carrier wave FM signal and a color signal component obtained by converting the low frequency converted color signal to a high frequency signal. are mixed again and output as a composite video signal.

By the way, when converting a low frequency converted color signal to a high frequency (normal subcarrier frequency), in order to reduce the amplitude noise received by the electromagnetic conversion system, the color signal amplifier is used so that the amplitude of the reference burst signal is constant. I was trying to control the gain.

[Problems to be Solved by the Invention] As mentioned above, in the conventional color signal processing circuit, the gain of the color signal amplifier is controlled so that the amplitude of the reference burst signal is constant. However, with this method, it was not possible to remove even the fine amplitude noise that the color information part received.

This invention was made to solve this problem, and it removes the amplitude noise of the color signal by limiting the amplitude so as not to destroy the amplitude information of the color signal and the amplitude of the reference burst signal. The object of the present invention is to provide a color signal processing circuit that can obtain the following color signal processing circuits.

[Means for Solving the Problems] A color signal processing device according to the present invention detects the amplitude of a color signal output from a signal source, generates a signal proportional to this amplitude, and generates a signal proportional to this amplitude. The amplitude of the color signal is limited by a threshold according to the level of the color signal, and a reference burst signal whose amplitude is not limited is output during the period of the reference burst signal in the color signal.

[Operation] In the present invention, the threshold value in the variable amplitude limiting circuit changes depending on the output level of the level detection circuit. Therefore, the variable amplitude limiting circuit limits the amplitude of the color signal without destroying the amplitude information of the color signal. Further, the normal reference burst signal output means outputs a reference burst signal whose amplitude is not limited during the period of the reference burst signal in the color signal. Therefore, the amplitude of the reference burst signal is not limited.

[Embodiment] FIG. 1 is a schematic block diagram showing an embodiment of the present invention. In the figure, a signal source 1 generates a color signal with a reference burst signal. This color signal is applied to the level detection circuit 2, the variable amplitude limiting circuit 3, and the switching circuit 17. Level detection circuit 2
is a circuit that detects the amplitude of a color signal and generates a signal proportional to the amplitude. The output of the level detection circuit 2 is given to a variable amplitude limiting circuit 3. The variable amplitude limiting circuit 3 is a circuit that limits the amplitude of the color signal from the signal source 1, and its threshold value is configured to change according to the level of the output signal of the level detection circuit 2. The output of the variable amplitude limiting circuit 3 is given to a switching circuit 17. Furthermore, switching circuit 1
7, a burst gate pulse 18 which is at a high level (or low level) only during the period of the reference burst signal of the color signal is applied as a switching control signal. The switching circuit 17 is switched by the burst gate pulse 18 to output the output signal of the signal source 1 during the reference burst signal period and to output the amplitude limited output signal from the variable amplitude limiting circuit 3 during other periods. . The output of the switching circuit 17 is applied to a load circuit 4 such as a color signal/luminance signal mixing circuit.

FIG. 2 is a circuit diagram showing a more detailed configuration of the embodiment shown in FIG. 1. In the figure, the level detection circuit 2 includes a capacitor 20, a resistor 21, a bias voltage source 22, a rectifier diode 23,
It includes a discharge resistor 24 and a smoothing capacitor 25. One end of the capacitor 20 is connected to the signal source 1, and the other end is grounded via a resistor 21 and a bias voltage source 22. Also, capacitor 20
The other end is connected to the variable amplitude limiting circuit 3 via the anode and cathode of the rectifying diode 23. Discharge resistor 24 is interposed between the cathode of rectifier diode 23 and ground. Similarly, the smoothing capacitor 25 is interposed between the cathode of the rectifying diode 23 and ground.

The variable amplitude limiting circuit 3 includes a capacitor 30, a resistor 31, and bias voltage sources 32, 36, 37.
, a limiting resistor 33, a subtracting circuit 34, an adding circuit 35, and amplitude limiting diodes 38 and 39. The color signal from signal source 1 is connected to capacitor 30
given at one end. The resistor 31 and bias voltage source 32 are connected in series and inserted between the other end of the capacitor 30 and ground. One end of the resistor 33 is connected to the other end of the capacitor 30, and the other end is connected to the cathode and anode of the switching circuit 17 and amplitude limiting diodes 38 and 39. On the other hand, the output of the level detection circuit 2 is applied to a negative input terminal of the subtraction circuit 34 and one input terminal of the addition circuit 35. Further, bias voltage sources 36 and 37 are connected to the positive input terminal of the subtraction circuit 34 and the other input terminal of the addition circuit 35, respectively. The output of the subtraction circuit 34 is applied to the anode of an amplitude limiting diode 38. The output of the adder circuit 35 is applied to the cathode of an amplitude limiting diode 39.

FIG. 3 is a graph showing the input/output characteristics of the above-mentioned embodiment, where the horizontal axis represents the input signal amplitude (amplitude of the output signal V _s of signal source 1), and the vertical axis represents the output signal amplitude (variable amplitude limiting circuit). The amplitude of the output signal of 3) is taken. FIG. 4 is a waveform diagram of signals at each part of the embodiment shown in FIGS.
The waveform of the output signal V _s of the level detection circuit 2, the waveform of the output signal V _d of the level detection circuit 2, and the burst gate pulse 18
, and the waveform of the output signal V _p of the switching circuit 17 are shown. The operation of the above-described embodiment will be explained below with reference to FIGS. 3 and 4.

First, a color signal output from a signal source 1 is given to a level detection circuit 2 and a variable amplitude limiting circuit 3. The color signal input to the level detection circuit 2 is
A bias voltage is applied by a bias voltage source 22, and the amplitude is detected by a rectifier diode 23. This detected voltage is smoothed by a smoothing capacitor 25 and taken out as a DC voltage _Vd proportional to the level of the color signal _Vs , as shown in FIG.

A bias voltage is added to the color signal supplied from the signal source 1 to the variable amplitude limiting circuit 3 by a bias voltage source 32, and the color signal is supplied to the switching circuit 17 after passing through a limiting resistor 33. At this time, the addition circuit 35
outputs a DC voltage proportional to the output signal V _d of the level detection circuit 2, and the subtraction circuit 34 outputs a DC voltage inversely proportional to the output signal V _d of the level detection circuit 2. The output voltage V _HL of the addition circuit 35 and the output voltage V _LL of the subtraction circuit 34 are
Amplitude limiting diodes 15 and 16 are operated to limit signal amplitude noise of the color signal passing through limiting resistor 33. That is, when the level of the color signal exceeds the output voltage V _HL of the adder circuit 35, the diode 39 becomes conductive and the level of the color signal is lowered to the voltage V _HL . On the other hand, the level of the color signal is
When the output voltage of 4 drops below V _LL , diode 3
8 becomes conductive and the level of the color signal is raised to the voltage _VLL . That is, the diodes 38 and 39 function as a so-called limiter circuit. The threshold value of this limiter circuit is changed by the output voltage of the level detection circuit 2 (see FIG. 3).

The switching circuit 17 outputs the color signal from the signal source 1 as it is during the reference burst signal period, and outputs the color signal from the signal source 1 as it is during the reference burst signal period, and outputs the color signal from the variable amplitude limiting circuit 3 as it is during the period of the reference burst signal, in response to the burst gate pulse 18 indicating that it is the reference burst signal period. It works to output the output of . Therefore, the reference burst signal is supplied to the load circuit 4 as it is from the signal source 1. The reason for this configuration is to prevent the reference amplitude and phase from changing by limiting the amplitude of the reference burst signal.

In the above embodiment, the case of a color signal reproducing circuit of a VTR was explained, but the present invention can be applied to other devices that write a video signal in some form on a recording medium and read it out.

Further, in the above-described embodiment, the reference burst signal whose amplitude is not limited is extracted by switching the switching circuit 17 with the burst gate pulse 18, but the output voltage of the level detection circuit 2 is changed over the reference burst signal period. It may also be possible to prevent the variable amplitude limiting circuit 3 from performing amplitude limiting by offsetting the signal by a certain amount. That is, when the output voltage of the level detection circuit 2 becomes sufficiently large due to the offset, the diodes 38 and 39 are not conductive and the amplitude is not limited even if the level of the reference burst signal becomes considerably large.

[Effects of the Invention] As described above, according to the present invention, the amplitude of the color signal is limited by a threshold value that corresponds to the amplitude level of the color signal, so that the color signal can be controlled without losing the color information of the color signal. Amplitude noise in the signal can be removed. Furthermore, since the reference burst signal whose amplitude is not limited is output during the reference burst signal period, it is possible to prevent the amplitude and phase of the burst signal, which is the reference for video reproduction, from changing.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram showing one embodiment of the present invention. FIG. 2 is a circuit diagram showing a more detailed configuration of the embodiment shown in FIG. 1. Figure 3 is the first
3 is a graph showing the input/output characteristics of the embodiment shown in FIG. 3 and FIG. 2. FIG. FIG. 4 shows a waveform diagram of signals at each part of the embodiment shown in FIG. In the figure, 1 is a signal source, 2 is a level detection circuit, 3 is a variable amplitude limiting circuit, 4 is a load circuit, 17
indicates a switching circuit.

Claims (1)

[Scope of Claims] 1. A color signal processing circuit for removing amplitude noise of a color signal, comprising: a signal source that generates a color signal having a reference burst signal; and an amplitude noise of the color signal output from the signal source. a level detection circuit that detects a signal and generates a signal having a level proportional to the detected amplitude, the threshold voltage of which changes according to the output level of the level detection circuit, and the amplitude of the color signal changes at the threshold value. A variable amplitude limiting circuit that outputs a signal whose amplitude is limited by the variable amplitude limiting circuit in a period other than the period width of the reference burst signal, and which outputs a signal whose amplitude is limited by the variable amplitude limiting circuit in a period other than the period width of the reference burst signal; A color signal processing circuit comprising a signal output means for outputting a color signal. 2. The signal output means includes a switching circuit that switches and outputs the output of the signal source and the output of the variable amplitude limiting circuit according to a signal indicating the period of the reference burst signal. The color signal processing circuit described in Section 1. 3. The signal output means includes means for disabling the amplitude limiting operation of the variable amplitude limiting circuit during the period of the reference burst signal.
The color signal processing circuit described in Section 1.