Dear SpiceMonkey, [quote userid="514962" url="~/cadence_technology_forums/f/custom-ic-design/49080/could-anyone-explain-this-sampled-noise-simulation-result/1378362#1378362"]Resistor is 920K rather than 920 posted before. I have revised the post. [/quote] Ahah! That makes more sense now to me - thank you for updating your post! However, my computation of 920K and 10 pF provides a first order low-pass filter cutoff frequency (-3 dB) of 17.3 kHz. I think your post suggests the -3 dB corner is 27 kHz. [quote userid="514962" url="~/cadence_technology_forums/f/custom-ic-design/49080/could-anyone-explain-this-sampled-noise-simulation-result"] f(RC) 27KHz, no alising should happen. (r=920K, c=10p)[/quote] Am I misinterpreting your data? [quote userid="514962" url="~/cadence_technology_forums/f/custom-ic-design/49080/could-anyone-explain-this-sampled-noise-simulation-result/1378362#1378362"]ou are correct! If I move the capacitor prior to the switch, then get the 4KTR density.[/quote] Excellent and great! Thank you for modifying your schematic and re-running the simulation! [quote userid="514962" url="~/cadence_technology_forums/f/custom-ic-design/49080/could-anyone-explain-this-sampled-noise-simulation-result/1378362#1378362"] have have read your PDF, it explains the aliasing well, thank you again! Im still trying to understand the principle behind this, quantitatively, maybe somtting about both "correlated" and "aliasing" [/quote] I am glad the document provided you some insight SpiceMonkey - great! With respect to your last comment concerning an understanding of the quantitative principle and the terms "correlated" and "aliasing", I must admit I am not fully understanding what you are looking for. I'll make an attempt to see if this helps at all.... You may consider the sampling switch as multiplying the analog signal by a series of time-delayed impulses. As this is a multiplication process in the time-domain, it represents a convolution operation of the two Fourier transforms (i.e. the Fourier transform of the signal and the Fourier transform for the series of sample pulses) in the frequency domain. A property of the sample function delayed by some value of tau is to place a copy of the signal's spectrum centered about the frequency corresponding to the frequency of 1/tau. Hence, if there are a series of impulses that periodically sample the analog signal every t= Ts, the analog spectrum of your signal is translated to appear at multiples of the frequency corresponding to Ts. Mathematically, this means the resulting spectrum of the sampled signal is from reference [1]: I hope this provides a bit more insight consistent with what you were looking for! Shawn Reference [1]: ece-research.unm.edu/.../sample.pdf
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