JPS62117485A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To remove noise superimposed on a black level and to prevent the error of data by inputting an output of a circuit for clamping the black level of a video signal to a comparison circuit through an LPF and clamping the black level by the comparison output. CONSTITUTION:The black level of the video signal in which a signal is outputted with a low impedance is clamped by a clamp circuit 1, and the output of the circuit 1 is inputted to the comparison circuit 2 through the low pass filter (LPF)6. In the circuit 2, the output voltage of the circuit 2 is compared with the voltage of a reference voltage source 3 and black level of the video signal is controlled to a constant value. The signal clamped by the reference potential of the output of the circuit 1 is sliced by a slice reference potential of a reference voltage source 5 in a slice circuit 4 and outputted as a signal of a constant amplitude.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a video signal processing circuit, and particularly to a video signal processing circuit that processes a video signal in a first
It also relates to a video signal processing circuit that outputs a signal with a width of (2) and a constant width by slicing it at a second reference potential.

[Conventional technology-1 Currently, television images 1't+ (r; Suno+liH
Digitizing character and graphic information between the lines 1.
/j-j--evening teletext broadcasting has been put into practical use.

In a character multiplex signal reproduction system, the 111r that decodes the digital information signal to the decoder 1 needs a function to accurately extract only the data part from the video (i3).

Fig. 2 shows the blocks of a data sampling circuit showing an example of a conventional video signal processing circuit 1''l!, l'jjl.
is manually applied to the clamp circuit 1. The output of the clamp circuit 1 is connected to one input terminal r- of the comparator circuit 2 and one input terminal of the slice circuit 4.

A quasi-voltage source 3 is connected to the local input terminal of the comparator circuit 2, and the output of the comparator circuit 2 changes the black level of the video signal to the clamp J, (quasi-potential V re ) of the reference voltage source 3.
The clamp circuit 1 is controlled so that it is equal to fl, and the black level at one input terminal of the slice circuit 4 is equal to the clamp reference potential Vre, and the signal ■2' clamped at the moon.
or can be obtained. This signal V2' is sliced in the slicing circuit 4 at the slice store quasi-potential Vr-2 of the reference voltage source 5, and an output signal 3 is obtained.

[Problems to be Solved by the Invention] In the conventional data acquisition circuit described above, the output signal of the clamp circuit is directly input to the comparison circuit that sets the clamp level, so noise is generated when receiving a weak electric field video signal. be influenced by. As a result, if noise is superimposed on the black level at the input of the comparator circuit, accurate black level clubbing operation will not be performed, so the input signal data will not be sliced at the set reference potential in the slicing circuit, and the output signal data will not be sliced. There is a problem with errors occurring.

In the conventional television video signal processing circuit, a 3.58M)12 trap circuit is connected to remove the chroma signal component, and as a result, the frequency characteristics can be lowered and the noise component can be blocked. etc., b<feed'1. The data frequency that comes is about 6 MI
Since the IZ and high frequencies are high, inserting a 1-wrap circuit or filter '4 as described above in the path will cause the frequency characteristics to deteriorate and there is a risk that accurate (1T) transmission will not be possible. Yes 1.;C also has a drawback that causes hazy operation.

[Means for Solving the Problem 6] The video signal processing circuit of the present invention includes a clamp circuit that clamps the black level of the video signal i3 whose signal is output with low impedance, and a a comparison circuit that compares a first reference potential; and a slicing circuit that slices the output of the clamp circuit, in which the black level of the video signal is clamped at the first reference potential by the output of the comparison circuit, at a second reference potential. , the output of the clamp circuit and Ojr
and a low-pass filter connected between the input of the comparison circuit and the input of the comparison circuit.

〔Example〕

Next, the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the image signal processing circuit of the present invention, and FIG. 3 is for explaining the operation of FIG. 1. FIG.

In the first country, the same components as in the conventional example are given the same reference numerals as in FIG. , a comparison circuit 2 that compares the output of the clamp circuit 1 and the clamp reference potential Vrefl, and a club circuit 1 in which the black level of the video signal is clamped at the clamp reference potential Vrerl by the output of the comparison circuit 2.
In the conventional example, a low-pass filter 6 is inserted and connected between the output of the clamp circuit 1 and one input of the comparator circuit 2.

Next, the operation of this embodiment will be explained with reference to FIG.

A video signal (1) on which character/graphic information data is multiplexed is input to the clamp circuit 1. The output of the clamp circuit 1 is inputted to one input terminal of the comparator circuit 2 via the low-pass filter 6, and is connected to the other input terminal -r of the comparator circuit 2. (?llj The clamp reference potential V of the voltage source 3 is compared with the clamp reference potential V . At the end of person 71, the black bell is the clamp reference potential V
A signal (2) clamped by rarl is obtained. This signal (2) is sliced by the slice reference potential V ref2 of the reference voltage source 5 in the slice circuit 4, and
3 is obtained.

[Effects of the Invention] As explained above, the present invention provides an image processing system by connecting a low-pass filter between the input terminal of the comparator circuit that sets the clamp reference level of the black level clamp circuit that measures one image, and the output terminal of the clamp circuit. The noise component superimposed on the signal black level is blocked at the input terminal of the comparison circuit 1t1? In addition, since there is no deterioration of frequency characteristics caused by a low-pass filter in the signal transmission path to the slice circuit, high-frequency signals can be transmitted accurately. It has the effect of being able to

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the video signal processing circuit of the present invention, Fig. 2 is a process diagram of a data sampling circuit showing an example of a conventional video signal processing circuit, FIG. 3 is a signal waveform diagram for explaining the operation shown in the figure. 1...clamp circuit, 2...comparison circuit, 5...
- Reference voltage source, 4... slice circuit, 6... low pass filter.

Claims (1)

[Claims] a clamp circuit that clamps the black level of a video signal whose signal is output at low impedance; a comparison circuit that compares the output of the clamp circuit with a first reference potential; and a slicing circuit that slices the output of the clamp circuit clamped at the first reference potential at a second reference potential, between the output of the clamp circuit and the input of the comparison circuit. A video signal processing circuit characterized by having a low pass filter connected to.