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Delta-Sigma .DELTA.-.SIGMA. modulator having a dynamically tunable continuous time Gm-C architecture

  • US 5,729,230 A
  • Filed: 01/17/1996
  • Issued: 03/17/1998
  • Est. Priority Date: 01/17/1996
  • Status: Expired due to Term
First Claim
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1. A tunable Delta Sigma (Δ

  • Σ

    ), modulator comprising;

    an input transconductance cell that converts an analog voltage signal, which has a signal spectrum that occupies a known bandwidth, into an analog current signal at a first summing node;

    a tunable resonator that is connected to the first summing node and generates an integrated voltage signal at a second summing node;

    a quantizer that oversamples the integrated voltage signal and converts it into a digital output voltage signal, said output voltage signal having an output spectrum that is the sum of the signal spectrum and a quantization noise spectrum;

    a feedback path which returns said digital output voltage signal to the first and second summing nodes; and

    a digital-to-analog converter (DAC) in the feedback path that converts said digital output voltage signal into reproducible current levels;

    said tunable resonator having a resonant frequency ω

    0 that is tunable to shape the quantization noise spectrum to reduce the quantization noise in said output spectrum over the known bandwidth, said tunable resonator comprising;

    a pair of integrating capacitors having capacitances C1 and C2 that are connected at the first and second summing nodes, respectively;

    a fixed transconductance cell having transconductance G1 that is connected between the first and second summing nodes; and

    a tunable transconductance cell having a variable transconductance GT that is connected between the first and second summing nodes in an anti-parallel configuration with said fixed transconductance cell,said resonator having a frequency response H(s) of;

    ##EQU11## where ω

    0= (G1GT)/(C1C2)!0.5.

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