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Sigma-delta modulator

  • US 5,103,228 A
  • Filed: 06/10/1991
  • Issued: 04/07/1992
  • Est. Priority Date: 06/22/1990
  • Status: Expired due to Fees
First Claim
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1. Sigma-delta modulator for converting an input signal into a 1-bit digital output signal, comprising:

  • a low-pass filter including a series connection of first, second and third sections having at least first order filter functions, each section having an input and having an output for producing respective first, second and third section signals;

    quantization means for converting the third section signal into the 1-bit digital output signal and for producing first and second feedback signals in response to the digital output signal;

    a first subtractor stage for producing a first difference signal from the second section signal and the first feedback signal and for applying the first difference signal to the input of the third filter section;

    a second subtractor stage for producing a second difference signal form the input signal and the second feedback signal and for applying the second difference signal to the input of the first filter section; and

    coupling means for coupling the first section signal to the input of the second filter section,characterized in that the first and third filter sections as regards the signal frequencies are arranged as passive networks, and in that the second filter section is arranged as an active filter stage.

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