US 2006/0077303 A1 · Method and apparatus to improve ADC dynamic range in a video decoder

Abstract

A video decoder in which 1) resolution quality can be improved for a given bit count analog-to-digital converter, 2) a lower bit count analog-to-digital converter can be used with substantially similar quality or 3) a combination of improved resolution quality with a lower bit count analog-to-digital converter can be done. In the preferred embodiment, a DC bias is added to the video signal after the sync portion of the composite signal has been received and prior to the active video being received. This bias is then removed after the end of the active video period. By applying this bias, the DC voltage level of the video signals is actually reduced, so that the full scale value of the analog-to-digital conversion process can also be reduced. Thus, compared to using an unbiased signal, increased A/D converter resolution is obtained. In an alternative embodiment, the sync portion can be biased upwardly during the front porch and then be returned during the back porch.

Claims21

Dependent claims

A system to improve dynamic range of an analog to digital conversion of a composite video signal, the system comprising:

a video signal input for receiving an analog composite video signal;
a gain control amplifier coupled to said video signal input and having a gain control amplifier output;
a sample and hold circuit having a sample and hold circuit input coupled to said gain control amplifier output and having a sample and hold circuit output;
a DC level shift circuit connected to said sample and hold circuit input to DC shift a portion of said gain control amplifier output to reduce the full maximum voltage swing of said sample and hold circuit output to a reduced maximum voltage swing;
and
an analog to digital converter having an input coupled to said sample and hold circuit output, having a reference voltage related to the reduced maximum voltage swing rather than the full maximum voltage swing and having an analog to digital converter output.

3 more elements

An analog video decoder comprising:

a system to improve dynamic range of an analog to digital conversion of a composite video signal, the system including:
a video signal input for receiving an analog composite video signal;
a gain control amplifier coupled to said video signal input and having a gain control amplifier output;
a sample and hold circuit having a sample and hold circuit input coupled to said gain control amplifier output and having a sample and hold circuit output;
a DC level shift circuit connected to said sample and hold circuit input to DC shift a portion of said gain control amplifier output to reduce the full maximum voltage swing of said sample and hold circuit output to a reduced maximum voltage swing;
and
an analog to digital converter having an analog-to-digital converter input coupled to said sample and hold circuit output, having a reference voltage related to the reduced maximum voltage swing rather than the full maximum voltage swing;
and having an analog-to-digital converter output;
a filter having a filter input coupled to said analog to digital converter output and providing a filter output;
a composite decoder having a composite decoder input coupled to said filter output and providing a composite decoder output;
a digital formatter having a digital formatter input coupled to said composite decoder output and providing a digital video signal output;
a low pass filter having a low pass filter input coupled to said analog to digital converter output and providing a low pass filter output;
a sync detector circuit having a sync detector circuit input coupled to said low pass filter output and providing horizontal and vertical sync outputs;
and
a clock generator having a clock generator input coupled to said low pass filter output and providing a source locked clock output.

12 more elements

An analog video decoder comprising:

a system to improve dynamic range of an analog to digital conversion of a composite video signal, the system including:
a video signal input for receiving an analog composite video signal;
a sample and hold circuit coupled to said video signal input and having a sample and hold circuit output;
a DC level shift circuit connected to said sample and hold circuit input to DC shift a portion of said sample and hold circuit input to reduce the full maximum voltage swing of said sample and hold circuit output to a reduced maximum voltage swing;
and
an analog to digital converter having an analog to digital converter input coupled to said sample and hold circuit output, having a reference voltage related to the reduced maximum voltage swing rather than the full maximum voltage swing and having an analog to digital converter output;
a filter having a filter input coupled to said analog to digital converter output and providing a filter output;
a composite decoder having a composite decoder input coupled to said filter output and providing a composite decoder output;
a digital formatter having a digital formatter input coupled to said composite decoder output and providing a digital video signal output;
a low pass filter having a low pass filter input coupled to said analog to digital converter output and providing a low pass filter output;
a sync detector circuit having a sync detector circuit input coupled to said low pass filter output and providing horizontal and vertical sync outputs;
and
a clock generator having a clock generator input coupled to said low pass filter output and providing a source locked clock output.

10 more elements

Dependencies are inferred from the claim text.

Method and apparatus to improve ADC dynamic range in a video decoder

Life of this patent

Method and apparatus to improve ADC dynamic range in a video decoder

Life of this patent

Abstract

Claims21