charge pump里面的opAMP起什么作用？

kmchen3089

about your question (回復 #1 adele 的帖子)
please refer to Razavi's Design of analog CMOS IC  textbook
edition 2001 ,page 567  & figure 15.47
it's to minimize charge sharing and can decrease vco input ripple voltage
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The structure is originally presented on JSSC,vol.SC-23,pp1218-1223,October 1988 (see figure 8 on this paper)
A variable delay line pll for CPU-coprocessor synchronization