Hello,
I have an integrator circuit that is reset periodically. Right before the reset, a sample is taken on which I would like to calculate the noise.
Conceptually, after the reset, the system is not in steady state and the output (noise) variance will grow until the system reaches steady-state.
The noise analysis gives me the steady state result. The output noise is attached at the end and the total integrated noise is 125uVrms.
Now I run pss+pnoise with tdnoise and plot the total integrated noise vs. time. This is what the outcome looks like:
Except for the y-axis scaling exactly as expected! The waveform of the reset signal is clearly visible: The system is reset between about 0 and 70ns, then the integrator starts and the total noise increases. It reaches a maximum at 250ns=0ns; then it is reset again.
However, this shows the plot for different values of "Integration Stop Frequency". 4MHz, 1PHz, 10PHz, 100PHz, 1000PHz:
Dependening on which value I choose for the stop frequency I can make the total noise shift arbitrarily. This does not make sense to me. For noise it's clearly visible that the system is bandlimited so the total noise must converge to a fixed number. Furthermore, it must be always smaller than the value in steady state (125uVrms from .noise). Particularly, when I make the number of sidebands (and maxacfreq in pss) very high, the number must converge to the one from .noise.
Why is this? Are my settings wrong?
I use pss; beat freq=4MHz, number harmonics=49, moderate, maxacfreq=1G
pnoise: Start: 1, Stop: 100G (some very high number), 10pts per decade. Maximum sidebands: 51.
Finally I use ADE L -> Direct Plot -> tdnoise -> Integ Output Noise, Total Noise, Start Frequency 1 Hz and Stop Frequency I vary from 1 MHz .... 10000PHz with difference results (as above).
As can be inferred from the plots, the control signals run at 4 MHz with ~21:6 duty cycle.
PS: This is the .noise output. Total integrated: 125uVrms.
