Comments related to calculating SNR from SPICE output or measurement results when using MATLAB

Example, if the sampling frequency is 176 MHz we might set the input frequency to 2.93333 MHz and the simulation stop time as 3.068 us, or .tran 10p 3.268u 200n 10p UIC and Vin Vin 0 DC 0 SIN 2.5 2 2.933333MEG.

Having done all of these the SPICE-simulated SNR is still generally limited to < 50 dB (< 8-bits), not because of SPICE accuracy, but rather to keep the simulation time reasonable. To improve the SPICE-simulated SNR the tolerances, reltol and vntol, need to be reduced (say by a factor of 10). SPICE simulation is still useful to check connectivity, integrator output swing, and other basic behavior; however, the silicon will generally perform better, more in line with theory, than a SPICE simulation will indicate.

Additional Reading

Saxena, V., "K-Delta-1-Sigma Modulators for Wideband Analog-to-Digital Conversion.pdf," Doctoral Dissertation, Boise State University, April 2010.