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Dual-mode modulation systems and methods including oversampling of narrow bandwidth signals and DC offset compensation

  • US 6,535,561 B2
  • Filed: 09/11/1998
  • Issued: 03/18/2003
  • Est. Priority Date: 11/17/1997
  • Status: Expired due to Term
First Claim
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1. A dual-mode modulation system comprising:

  • means for sampling an applied signal;

    means for converting the sampled signal to an analog signal;

    means for low pass filtering the analog signal to produce a filtered analog signal, at least one of the means for converting and the means for low pass filtering introducing DC offset into the filtered analog signal;

    means for modulating the low pass filtered analog signal onto a carrier;

    means for compensating for the DC offset in the filtered analog signal that is introduced by the at least one of the means for converting and the means for low pass filtering;

    means for applying a first signal to the sampling means to thereby modulate the first signal on a carrier using the sampling means, the converting means and the low pass filtering means, and for applying a second signal of narrower bandwidth than the first signal to the sampling means to thereby sample the second signal and modulate the second signal on a carrier using the sampling means, the converting means and the low pass filtering means; and

    wherein the means for compensating further comprises;

    means for sensing the DC offset in the filtered analog signal;

    means for converting the sensed DC offset into a digital DC offset signal;

    means for subtracting the digital DC offset signal from the sampled signal, and for applying the sampled signal less the DC offset signal to the means for converting the digital input signal into an analog signal; and

    means for scaling the digital DC offset signal into a scaled digital DC offset signal;

    the means for subtracting being responsive to the means for scaling, to subtract the scaled digital DC offset signal from the sampled signal.

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