sigma delta modulator site:edaboard.com
for complex systems like sigma-delta modulator, simulation starts with system level (block level) with ideal blocks like gain and switches, for finding some block specs like op amp gain. usually system level sim. is done in matlab/simulink; simulink is simpler but slower but matlab codes are much faster-speed is essential for parameter sweeping for optimum design.
after finding some block specs it is possible to use more accurate models like switch resistance, clock overlaps, opamp bandwidth and slew rate in the same environment i.e. matlab/simulink.
if system level is successful, with the block specs known, u can design each block (like opamp and comparators) seprately with spice and in transistor level, finally using this blocks u can simulate all of the modulator.
NOTE: Before full transistor level sim. usually a semi-transistor level simulation is necessary with some blocks(opamp and cmparator) in transistor level and others like switches and clocks in system level i.e. ideal switches and pulse voltage source as clocks; this simulation is done in spice.
BEST!