
Design of SC Delta-Sigma Modulators for Multistandard RF Receivers
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the calculated minimum C
sampling
is equal to 0.044 pF when the SNR and V
ref
are set
to 70 dB and 1.25 V, respectively. And for DECT, the result is 0.17 pF (OSR = 64)
when the SNR and V
ref
are set to 90 dB and 1.25 V, respectively. Sometimes a smaller
reference voltage such as 1.0 V is used to further reduce the thermal noise.
As we can see, C
sampling
for GSM has the largest capacitance (0.6 pF), hence it
should be the bottom line. In this design, C
sampling
is chosen to be 0.72 pF to provide a
design margin. The sizes of the sampling capacitors in the second and third integra- ...