[quote userid="538772" url="~/cadence_technology_forums/f/custom-ic-design/51410/how-to-obtain-discrete-time-dt-response-from-a-switched-cap-sc-circuit-integrator/1383193#1383193"] Thus, is my following statement true or false: *) Repeating pattern => DT response *) No repeating pattern => CT response [/quote] If by "DT response" you mean the result of a sampled PAC analysis, it is clearly false (as you have shown with your own experiments). You really need to distinguish between the spectrum of a sampled signal and the transfer function resulting from a sampled PAC analyisis: [quote userid="4061" url="~/cadence_technology_forums/f/custom-ic-design/51410/how-to-obtain-discrete-time-dt-response-from-a-switched-cap-sc-circuit-integrator/1383093#1383093"] There is an important difference between the spectrum of a sampled signal and the result of a sampled PAC analysis. For a sampled signal, due to aliasing you generally don't know the original frequency of the signal (unless its bandwidth was limited before the sampler). Due to this, all possible frequencies are often shown in the spectrum, which automatically leads to the well-known repeating and symmetrical spectrum of a sampled signal. In sampled PAC analysis, however, the frequency of the input signal is known and is used as the x-axis for plotting the result. As a consequence, you will only see a repeating and symmetrical pattern if it is caused by the circuit itself, for example by a frequency-dependent circuit after aliasing by a sampler. [/quote] The sampled PAC analysis only looks at the output at the input frequency (because I chose maxsideband=0 as a parameter) and only plots it at this frequency. The fact that the sampled output signal could also be interpreted as coming from different (aliased) frequencies is not taken into account here. By the way, the normal PAC analysis with maxsideband=0 like in my example also only looks at the output signal at the input frequency. For a piecewise constant signal, there will be additional frequency components in the spectrum, possibly with much higher amplitudes. [quote userid="538772" url="~/cadence_technology_forums/f/custom-ic-design/51410/how-to-obtain-discrete-time-dt-response-from-a-switched-cap-sc-circuit-integrator/1383193#1383193"]But why the hell then Mr. Kundert has written in his (already above cited) article: “ You must understand up front the difference between the continuous-time and discrete time behavior of your circuit, and you must decide which behavior you are interested in. ”. [/quote] I believe that he was talking about the difference between a track-and-hold and a sample-and-hold. Sampled PAC analysis with Dirac impulses did not exist back then. At that time, I was emulating it with sampled PNOISE analysis and separate noise sources for every Nyquist band.
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