JPS61112418A - Analog-digital converting circuit of television signal system - Google Patents

Abstract

PURPOSE:To attain highly stable A/D conversion by utilizing a difference be tween a black level of a digital output signal from the A/D converter and a preset level to improve the stability against temperature change and external noise. CONSTITUTION:An analog video signal inputted to an input terminal is converted into a digital signal by an A/D converter 3 via a DC component rejection capacitor 2, the signal is fed to an adder 7 and inputted to a black level detector 4. The DC potential output of the black level detector 4 is subtracted from the reference level obtained from a reference level generator 5 by an adder 6 to obtain a difference with the preset level. The difference is added to a digital output signal from the A/D converter 3 by the adder 7 and the result is given to an output terminal 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an A/D conversion circuit in a television signal processing circuit.

[Conventional technology]

In a conventional A/D conversion circuit of this type, a clamp circuit and a synchronization separation circuit necessary for generating a clamp pulse were configured in an analog manner.

[Problem that the invention seeks to solve]

Since the A/D conversion circuit described above is constructed using analog circuits, the clamp level and clamp phase may change due to temperature changes or external noise, causing problems in terms of the stability of the digital signal after conversion. Rarely.

[Means for solving problems]

In view of the above points, the present invention has been made to solve such problems, and its purpose is to stably convert an analog signal into a digital signal with a simple configuration.
An object of the present invention is to provide an A/D conversion circuit for a television signal system that can perform highly stable A/D conversion.

Ninth to achieve such objects, the present invention provides DC component removal means for removing the Kfl component of an input analog signal, and analog-to-digital conversion means for converting the analog signal obtained by the DC component removal means into a digital signal. a black level detecting means for detecting the black level of the digital signal obtained by the analog-to-digital converting means; a means for obtaining a predetermined difference between the next level and the level obtained from the black level detecting means; level fixing means for adding the difference 1-* distribution digital signal obtained by the means to identify the black level of the video signal at the predetermined nine levels; The present invention comprises a clipping means for clipping, and a clamp pulse generation means for generating a clamp pulse from a signal clipped by the clipping means.

[Effect]

After removing the DC component of the input analog video signal, the A/D
In addition to the converter, the DC potential of the black level at the time of conversion is detected, and this detected potential is subtracted from the reference level to obtain the A/
Obtain the difference between the black level of the digital output signal from the D converter and a preset level, add that difference 'r A/1) to the output of the converter, and fix the black level of the signal to the preset level. and output it.

Further, only the synchronizing signal is fully extracted, a pulse indicating the phase of the black level is generated from this synchronizing signal, and this pulse is returned to the means for detecting all of the DC components of the black level for control.

〔Example" Embodiments of the present invention will be described in detail below based on the drawings.

The figure is a block diagram showing one embodiment of the present invention, and shows only the parts necessary for explanation.

In the figure, 1 is an input terminal to which an analog video signal is applied, 2 is a capacitor for removing the DC component of the analog video signal from this input terminal 1, and this capacitor 2 is a means for removing the DC component of the input analog signal. It consists of 3 is an A/D converter that converts the analog signal obtained by this means into a digital signal, and 4 is a black level detector that is a means for detecting the black level of the digital signal obtained by this A/D converter 3. , 5 is a reference level generator that generates a predetermined level, and 6 is an adder that receives the output of this reference level generator 5 and the output of the black level detector 4 as inputs. Together with the generator 5,
It constitutes means for subtracting the level obtained by the black level detector 4 from the predetermined level from the reference level generator 5 to obtain a difference. This adder adds the difference obtained by the reference level generator 5 and the adder 6 to the next digital signal obtained by the 7UA/D converter 3, and this adder 7 adds the difference obtained by the means for obtaining the level difference. is added to the digital signal to fix the black level of the video signal to a predetermined level.

8.9 is a clip level generator and a clip circuit which are means for clipping the signal obtained by the fixing means at a predetermined level; 10 is a sync signal obtained by the clip level generator 8 and the clip circuit 9; This black level phase detection pulse generator 10 is a means for generating a clamp pulse from a signal clipped by the clipping means. It consists of Reference numeral 11 is an output terminal for outputting a synchronization signal separated from the video signal.

Next, the operation of the embodiment shown in this figure will be explained.

First, the DC component of the analog video signal applied to the input terminal 1 is removed by the DC component removal capacitor 2.
The output is converted into a digital signal by the ADD converter 3. The digital signal converted by this A/D converter 3 is supplied to an adder 7 and also input to a black level detector 4, and the DC potential of the black level at the time of conversion is detected by this black level detector 4. This output is sent to adder 6
By subtracting from the reference level obtained from the reference level generator 5, the difference between the black level of the digital output signal from the A/D converter 3 and the predetermined level of the reference level generator 5 is obtained.

Next, the black level of the signal is determined in advance by multiplying the difference obtained by using the 7JO calculator 6 into the digital output signal from the A/D converter 3 by using the power Ω calculator 7. The signal is fixed at the level set and sent to the output terminal 11.

On the other hand, only the same IA signal is extracted by the clip level generator 8 and the clip circuit 9. From the synchronization signal, a pulse indicating the phase of the black level is generated from the black level phase detection pulse generator 10 and returned to the black level detector 4 to control the DC potential of the black level.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the entire A/D conversion circuit is formed using a digital system, including the clamp circuit and the synchronous separation circuit, without using complicated means. It has much higher stability against temperature changes and external noise than the clamp circuit and synchronous isolation circuit that was constructed with analog circuits, so it is possible to perform highly stable A/D conversion, so it is practical. The effect is enormous.

[Brief explanation of drawings]

The figure is a block diagram showing one example of the present invention. 2. Book e Capacitor for DC component removal, 3...A/
D converter, 4...black level detector, 5...reference level generator, 6. γ...Adder, 8...Clip level generator, 9...Clip circuit, 10...
...Black level phase detection pulse generator.

Claims (1)

[Claims] A DC component removing means for removing a DC component of an input analog signal; an analog-to-digital conversion means for converting the analog signal obtained by the DC component removing means into a digital signal; black level detection means for detecting the black level of the obtained digital signal; means for obtaining a difference between a predetermined level and the level obtained from the black level detection means; and a means for obtaining a difference obtained by the means. level fixing means for fixing the black level of the video signal at the predetermined level by adding it to the digital signal; clipping means for clipping the signal obtained by the level fixing means at the predetermined level; and a clamp pulse generating means for generating a clamp pulse from a signal clipped by the clipping means.
D conversion circuit.