Response to EDABoard question: ADC in Matlab simulink

I’ve put together a 2nd order continuous sigma-delta Simulink model as a starting point. This is the multi-port feedback configuration (feeds back into input of 1st and 2nd integrators). I tried a 1st-order sigma-delta, but it’s hard to demonstrate noise-shaping with a 1st order, since they are not chaotic enough. Even the 2nd order shows some limit cycles. The simulink model has these features:

  • Parameters
    F1 : gain of 1st integrator
    F2: gain of 2nd integrator
    A1/A2 (optional): models finite circuit gain of integrators
    fmod: frequency of input (sinusoid)
    acmag: amplitude of input
    tQ: sampling period of quantizer
    ncyc: number of cycles (of input) to analyze for FFT
    kcyc: number of cycles (of input) to leave for startup
  • single-bit quantizer
  • multi-point feeeback (requires 2 DAC’s)

I’ve also created a matlab file that runs this model and does an FFT on the output. This file runs the simulink model and plots an FFT of the output. I haven’t messed with the coefficients or anything, but it is a good starting point.