SAMPLED-DATA SIMULATION OF OVER-SAMPLED SIGMA-DELTA MODULATORS - Computer Methods for Analysis of Mixed-Mode Switching Circuits - page 198

sigma-delta modulator are implemented using stray-insensitive switched
capacitor technique with the resistance value given by [5]
where is the equivalent resistance of the switched capacitor network,
is the clock frequency and C is the value of the switched capacitor.
Again, the operational amplifiers are considered to be ideal. The spec-
trum of the modulator is shown in Fig.9.9. These results were obtained
by simulating the circuit for 74k clock cycles, discarding the first 10k
data points to remove any transients, and performing a post FFT anal-
ysis on the remaining 64k data points.
The signal-to-noise ratio of the modulator is obtained by performing
the preceding simulation with variable input amplitude. For each in-
put amplitude, the output of the modulator is obtained by performing
transient-FFT analyses and the signal-to-noise ratio (SNR) is calculated.