Let me see if I understand what you are saying. Can we assume a circuit like the one shown in Figure 1 in
http://designers-guide.com/Analysis/sc-filters.pdf, and further assume that the switch is opening and closing periodically?
What I heard you say is that you are performing a strobed noise analysis using SpectreRF's tdnoise option and that you ran two noise simulations, one that samples the noise when the switch is open and one that samples when the switch is closed. You found that the noise you measure when the switch is closed (sample) is larger than when the switch is open (hold). Is this correct? Is it substantially larger?
If this summary is correct, I am surprised. I would expect the noise levels to be basically the same. But at the same time, I don't understand your reasoning as to why this indicates that the switch is injecting noise when it's off. Could you explain that more fully?
Could you also tell me if you have tried disabling the clock and performing the same noise analysis. Does the switch still generate significant noise when it is always off?
One last question, is the anomalous noise you are seeing due to thermal noise sources or flicker noise sources?
-August