Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion
Patent
1993-12-29
1996-07-16
Hoff, Marc S.
Coded data generation or conversion
Analog to or from digital conversion
Analog to digital conversion
341156, H03M 136
Patent
active
055371140
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a analogue-digital converter.
It also relates to a slaving loop, usually called clamp or retroclamp, allowing the DC component of a video signal to be restored.
Analogue-digital converters are used in electronics when digital coding of the information takes place.
An analogue-digital converter (ADC) has the function of converting an analogue electrical quantity into digital data. This analogue electrical quantity may be either a voltage, or a current. As is known to the person skilled in the art, an n-bit analogue-digital converter delivers 2.sup.n combinations each having n bits of resolution. The precision of such a converter is given by the changing of the least-significant bit, denoted LSB. According to the prior art, this precision is the same whatever the value of the input quantity. Depending on the desired applications, this may represent a drawback. It is so, for example, in slaving loops using analogue-digital converters so as to restore the DC component of a video signal.
The operation of restoring the DC component has the aim of fixing the DC reference voltage of the video signal at a precise value. According to this operation, the video signal of each line is sampled over its DC component or black level. A fraction of each sample is picked off and compared with a reference value so as to generate an error signal which is reinjected, possibly after amplification, into the video signal.
Several method are known to the person skilled in the art for carrying out this operation, and in particular a digital method, according to which the DC component is picked off after conversion of the said signal into digital code.
As has already been mentioned, the DC level picked off at the output of the analogue-digital converter is then defined with a precision of .+-.1 LSB. The DC component then exhibits an oscillation of .+-.1 quantification bit around the datum value, which has the consequence of preventing it stabilizing.
The invention does not exhibit this drawback.
The subject of the present invention is an analogue-digital voltage converter comprising 2.sup.n -1 comparators making it possible to generate 2.sup.n different voltage levels when the input voltage varies, and a binary coding circuit comprising means for converting the 2.sup.m voltage levels into 2.sup.n binary codes each having n bits of resolution, characterized in that it comprises additional means making it possible to code the voltage contained in at least one range of variation of the input voltage into an item of information having a number of bits of resolution greater than n.
The subject of the present invention is also a loop for slaving the DC component of a video signal, characterized in that it contains an analogue-digital converter according to the invention.
One advantage of the invention is thus correctly to stabilize the level of the DC component.
Other characteristics and advantages of the invention will appear on reading a preferential embodiment, given with reference to the attached figures in which:
FIG. 1 describes an analogue-digital converter according to the prior art;
FIG. 2 describes a conversion curve of the converter described in FIG. 1;
FIG. 3 represents an example of an analogue-digital converter according to the invention;
FIG. 4 describes the conversion curve of the converter described in FIG. 3;
FIG. 5 represents an analogue-digital converter according to the preferential embodiment of the invention;
FIG. 6 represents an application of the converter described in FIG. 5;
Throughout the figures, the same references designate the same elements.
According to the embodiments of the invention described, the input analogue electrical quantity is a voltage. It is obvious that the invention also relates to other types of converters, and especially converters for which the input quantity is a current.
FIG. 1 describes an analogue-digital converter 100 according to the prior art. It takes the form of a converter known to the person skilled in the art under the name of flash converter. F
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"Thomson-CSF"
Hoff Marc S.
Plottel Roland
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