Analysis of 1/f noise in switched MOSFET circuits

Analysis of 1/f noise in MOSFET circuits is typically performed in the frequency domain using the standard stationary 1/f noise model. Recent experimental results, however, have shown that the estimates using this model can be quite inaccurate especially for switched circuits. In the case of a periodically switched transistor, measured 1/f noise power spectral density (psd) was shown to be significantly lower than the estimate using the standard 1/f noise model. For a ring oscillator, measured 1/f-induced phase noise psd was shown to be significantly lower than the estimate using the standard 1/f noise model. For a source follower reset circuit, measured 1/f noise power was also shown to be lower than the estimate using the standard 1/f model. In analyzing noise in the follower reset circuit using frequency-domain analysis, a low cutoff frequency that is inversely proportional to the circuit on-time is assumed. The choice of this low cutoff frequency is quite arbitrary and can cause significant inaccuracy in estimating noise power. Moreover, during reset, the circuit is not in steady state, and thus frequency-domain analysis does not apply. This paper proposes a nonstationary extension of the standard 1/f noise model, which allows us to analyze 1/f noise in switched MOSFET circuits more accurately. Using our model, we analyze noise for the three aforementioned switched circuit examples and obtain results that are consistent with the reported measurements.