Video receiver with DC offset cancellation
An analog video receiver implemented in an integrated circuit device. The analog video receiver includes a mixing circuit to mix an analog video signal with a sinusoid to generate a frequency-shifted analog video signal, and an offset cancellation circuit to obtain a sample of the frequency-shifted analog video signal during a first time interval and, based on the sample, generate an offset cancellation signal that, when summed with the frequency-shifted analog video signal, reduces a substantially time-invariant offset in the frequency-shifted analog video signal.
1. A video receiver formed within an integrated circuit device, the video receiver comprising:
a mixing circuit to mix an analog video signal with a sinusoid to generate a frequency-shifted analog video signal;
an offset cancellation circuit to obtain a sample of the frequency-shifted analog video signal during a first time interval and, based on the sample, generate an offset cancellation signal that, when summed with the frequency-shifted analog video signal, reduces a substantially time-invariant offset in the frequency-shifted analog video signal; and
wherein the first time interval is a blanking interval indicated by at least one of a horizontal or a vertical synchronization component of the frequency-shifted analog video signal.
2. The video receiver of claim 1 wherein the substantially time-invariant offset comprises a direct-current (DC) voltage offset.
3. The video receiver of claim 1 wherein the frequency-shifted analog video signal is a differential video signal, and wherein the offset cancellation circuit comprises a differential amplifier having differential inputs coupled to receive respective component signals of the differential video signal, and differential outputs to generate a differential offset-cancellation voltage having an amplitude in proportion to an amplitude of the substantially time-invariant offset.
4. The video receiver of claim 3 further comprising a signal combination circuit to subtract the offset-cancellation voltage from the differential video signal to reduce the substantially time-invariant offset.
5. The video receiver of claim 1 further comprising an input node to receive the analog video signal and a switch to decouple the input node from an input of the mixing circuit during at least a portion of the first time interval.
6. The video receiver of claim 5 wherein the switch comprises a transistor switch.
7. The video receiver of claim 5 further comprising a timing circuit to assert a control signal during the first time interval to enable the offset cancellation circuit to sample the frequency-shifted analog video signal and to open the switch.
8. A method of operation within an integrated circuit device, the method comprising:
mixing an analog video signal with a sinusoid to generate a frequency-shifted analog video signal;
obtaining a sample of the frequency-shifted analog video signal during a first time interval, wherein the first time interval is a blanking interval indicated by at least one of a horizontal or a vertical synchronization component of the frequency-shifted analog video signal;
generating an offset cancellation signal based on the sample of the frequency-shifted analog video signal; and
summing the offset cancellation signal with the frequency-shifted analog video signal to reduce a substantially time-invariant offset in the frequency-shifted analog video signal.
9. The method of claim 8 wherein mixing the analog video signal with a sinusoid comprises mixing the analog video signal with a complex sinusoid having a frequency substantially equal to a carrier frequency of the analog video signal.
10. The method of claim 8 wherein generating an offset cancellation signal based on the sample of the frequency-shifted analog video signal comprises generating an offset voltage in proportion to an offset voltage present in the sample of the frequency-shifted analog video signal.
11. The method of claim 10 wherein summing the offset cancellation signal with the frequency-shifted analog video signal comprises subtracting the offset voltage from the frequency-shifted analog video signal in a summing circuit.
12. The method of claim 10 wherein summing the offset cancellation signal with the frequency-shifted analog video signal comprises adjusting a current flow that corresponds to the frequency-shifted analog video signal in accordance with the offset cancellation signal.
13. The method of claim 8 further comprising interrupting a signal pat used to receive the analog video signal during the first time interval.
14. The method of claim 13 wherein interrupting a signal path used to receive the analog video signal comprises transitioning a transistor switch from a conducting state to a substantially non-conducting state.
15. A video receiver comprising:
means for mixing an analog video signal with a sinusoid to generate a frequency-shifted analog video signal;
means for obtaining a sample of the frequency-shifted analog video signal during a first time interval, wherein the first time interval is a blanking interval indicated by at least one of a horizontal or a vertical synchronization component of the frequency-shifted analog video signal;
means for generating an offset cancellation signal based on the sample of the frequency-shifted analog video signal; and
means for summing the offset cancellation signal with the frequency-shifted analog video signal to reduce an offset in the frequency-shifted analog video signal.
16. A video receiver formed within an integrated circuit device, the video receiver comprising:
a mixing circuit to mix an analog video signal with a sinusoid to generate a frequency-shifted analog video signal;
an offset cancellation circuit to obtain a sample of the frequency-shifted analog video signal during a first time interval and, based on the sample, generate an offset cancellation signal that, when summed with the frequency-shifted analog video signal, reduces a substantially time-invariant offset in the frequency-shifted analog video signal; and
wherein the frequency-shifted analog video signal is a differential video signal, and
wherein the offset cancellation circuit comprises a differential amplifier having differential inputs caupled to receive respective component signals of the differential video signal, and differential outputs to generate a differential offset-cancellation voltage having an amplitude in proportion to an amplitude of the substantially time-invariant offset.
17. The video receiver of claim 16 further comprising a signal combination circuit to subtract the offset-cancellation voltage from the differential video signal to reduce the substantially time-invariant offset.
18. The video receiver of claim 16 further comprising an input node to receive the analog video signal and a switch to decouple the input node from an input of the mixing circuit during at least a portion of the first time interval.
19. The video receiver of claim 18 wherein the switch comprises a transistor switch.
20. The video receiver of claim 18 further comprising a timing circuit to assert a control signal during the first time interval to enable the offset cancellation circuit to sample the frequency-shifted analog video signal and to open the switch.
21. The video receiver of claim 16 wherein the substantially time-invariant offset comprises a direct-current (DC) voltage offset.