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Integral switched capacitor FIR filter/digital-to-analog converter for sigma-delta encoded digital audio

  • US 5,012,245 A
  • Filed: 10/04/1989
  • Issued: 04/30/1991
  • Est. Priority Date: 10/04/1989
  • Status: Expired due to Term
First Claim
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1. In an integrated circuit, a circuit for converting single bit digital input data into analog form, characterized by:

  • a shift register, having N-taps, for shifting the digital input data;

    a plurality of signal capacitors, corresponding to the taps on the shift register, each signal capacitor having a predetermined capacitance and one end coupling to a summing node; and

    ,a 2×

    2 switch, responsive to the corresponding tap on the shift register, having two inputs for selectively coupling one of two voltage references to the other end of the signal capacitors depending on the state of the corresponding tap of the shift register and two outputs;

    a 2;

    1 switch for coupling the corresponding one of the plurality of signal capacitors to either of the outputs of the 2×

    2 switch in response to the state of a clock signal;

    wherein signals on the summing node are analog signals corresponding to the digital input data and the capacitances of the signal capacitors represent corresponding tap weight coefficients of a finite impulse response filter.

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