Error feedback structure for delta-sigma modulators with improved stability
An error feedback circuit includes a first summer receiving an analog input signal and a feedback signal and outputting a summed signal. A quantizer receives the summed signal and outputs a quantized output signal. A limiter receives the summed signal and outputs a limited summed signal. The limiter limits the limited summed signal to α* (maximum value of input signal), α>1. A second summer receives the limited summed signal and the output signal and outputs an error signal. A filter receives the error signal and outputting the feedback signal. Typically, 1.0<α<2.0, more preferably 1.4<α<1.6. The filter has a transfer function of H 1 (z)=2z −1 −z −2 .
1. A method for improving stability of delta-sigma modulation process, comprising:
(a) receiving an analog input signal and a feedback signal;
(b) summing the received analog and feedback signal to produce a summed signal, wherein the summed signal is limited such that the absolute value of a limited summed signal has the value α*(maximum value of the input signal), α>1;
(c) quantizing the summed signal and outputting a quantized output signal;
(d) generating an error signal by summing the limited summed signal and the quantized output signal,
and
(e) performing second order filtering of the error signal to produce the feedback signal.
2. The method of claim 1 , wherein 1.0<α<2.0.
3. The method of claim 1 , wherein 1.4<α<1.6.
4. The method of claim 1 , further comprising performing the second order filtering using a transfer function H 1 (z)=2z −1 −z −2 .