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发表于 2010-3-6 23:58:58
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Abstracr-The design considerations for fast-settling operational ampli-
fiers(opamps)are significantly different between sampled-data switched-
capacitor(SC)and conventional continuous-time applications.In SC cir-
cuits,the shape of the output voltage waveform of an opamp is of no
consequence provided that the output settles to within a specified tolerance
of its steady-state value prior to the next sampling instant.This feature
allows for an optimum opamp frequency shaping to obtain a minimum
small-signal settling time.The theory applies to any opamp that is well
approximated by a two-pole model,including the conventional two-stage
and single-stage folded-cascode topologies.As the commonly-used equiva-
lent-circuit Miller-effect model for frequency compensation has generally
been improperly applied to two-stage transconductance amplifiers,it does
not provide sufficient accuracy to achieve the optimum phase margin
condition.Therefore,the use of equivalent-circuit models has been refined
to provide greater accuracy and to eliminate some previous misconcep-
tions.
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