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DC offset cancellation circuits and methods

  • US 7,477,885 B2
  • Filed: 04/22/2005
  • Issued: 01/13/2009
  • Est. Priority Date: 04/22/2005
  • Status: Active Grant
First Claim
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1. A wireless receiver comprising:

  • a mixer having a first input, a second input and an output, wherein the first input is coupled to a first amplifier to receive an amplified RF signal and the second input is coupled to a frequency synthesizer to receive a first signal having one of a plurality of frequencies; and

    a plurality of parallel DC offset cancellation stages selectively coupled to the mixer output,wherein if the first signal has a first frequency, then a first one of the plurality of parallel DC offset cancellation stages is coupled to the mixer output, and if the first signal has a second frequency, then a second one of the plurality of parallel DC offset cancellation stages is coupled to the mixer output,wherein, in a first state, at least one of the DC offset cancellation stages has a first low cutoff frequency and, in a second state, the at least one DC offset cancellation stage has a second low cutoff frequency less than the first low cutoff frequency,wherein each of the plurality of stages is coupled to a first resistance in the first state, and each of the plurality of stages is coupled to a second resistance greater than the first resistance in the second state.

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