
Demystifying Switched-Capacitor Circuits
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and the SNR is degraded accordingly. Eventually, the SNR may drop to or even
below zero.
To test whether a ∆Σ modulator is stable or not, we can examine its output
sequence in the time-domain (i.e., looking for long 1’s or −1’s). Alternatively, we can
use a spectrum analyzer or a computer with a data acquisition kit to record its output
sequence and then plot the “SNR vs. input frequency” curve using the fast Fourier
transform (FFT). If we fi nd an abrupt drop of SNR in the curve, then the modulator
is likely to be unstable.
The design of a high-order (L > 2) and 1-bit-quantization ∆Σ modulator with a ...