Hi,
  I am simulating a 10 bit ADC with Cadence AMS simulator using Spectre as the solver for the analog part. When I simulate the design for a short period 100 us, the output is as expected. However, when I increase the simulation time above 1 ms, the output becomes inaccurate. It displays some kind of ripple at about twice the sampling frequency. I attached screen shot of the two cases. The purple waveform is when I set the simulator to simulate for 1.024us. The yellow waveform if when I set the simulator for 65 us.
I already tried to switch between pure Spectre and APS mode. I also tried to reduce the max_step parameter down to 100 ps without any impact on the simulator output (except increasing simulation time). I am strobing the output at 1 us interval since it is a MS/s ADC. What parameter/option should I use to tell Spectre to be as accurate for a short and long simulaton?