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CMFB effect on slew rate of Fully differential amplifier

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phanikiran

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When i am doing slew rate analysis for a fully differential amlfier, at the output , i am not getting a proper rising or falling pulse, it's rising , falling and again rising. i tried to slove it by increasing the gain and UGB of CMFB, but it's not working. But by removing CMFB its proper. How the CMFB affects the slew rate of a fully differential amplifier.
 

phanikiran said:
i tried to slove it by increasing the gain and UGB of CMFB, but it's not working. But by removing CMFB its proper. How the CMFB affects the slew rate of a fully differential amplifier.
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Of course UGB and slew rate of the CMFB itself affect the behavior of the diff amp: if the CMFB isn't fast enough, some nodes of the diff amp can temporarily get outside of their common mode range. This could be the reason for multiple edges. Check the control node and output nodes of the amp during the edge(s).
 

You can eliminate this problem due to the CMFB (CMFB wont come into picture when there is no change in the common modes) by giving perfectly differential input pulses to measure the slew rate of the opamp.
 

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