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Method and arrangement for a sigma delta converter for bandpass signals

  • US 4,857,928 A
  • Filed: 01/28/1988
  • Issued: 08/15/1989
  • Est. Priority Date: 01/28/1988
  • Status: Expired due to Term
First Claim
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1. An apparatus for converting a signal having a non-zero frequency carrier or suppressed carrier with modulation thereon from an analog signal to a digital signal with improved signal-to-noise ratio performance, the apparatus comprising:

  • (a) bandpass filtering means, having an input coupled to a first summing node, an output coupled to a positive input of a second summing node, and having an associated damped sinusoidal impulse response therein, for filtering the analog signal before applying it to the second summing node;

    (b) n-level quantizing means, having an input coupled to said second summing node, for quantizing the analog signal into a digital signal by oversampling and providing a digital signal having a plurality of levels (n) at an output therefrom;

    (c) n-level D/A converting means, having an input coupled to the output from said quantizing means and having an output coupled to said first summing node, for converting said n-level digital signal back to an analog signal to provide a negative feedback signal to the first summing node for providing improved signal-to-noise ratio perforrmance; and

    (d) direct current (DC) feedback means, having an input coupled to the output of said D/A converting means and an output coupled to a negative input of said second summing node, for feeding back a DC voltage to minimize DC offset voltages within the apparatus.

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