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AC response & step response simulation of a switched-capacitor amplifier (Read 1856 times)

rajeee1000

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Bangalore

AC response & step response simulation of a switched-capacitor amplifier
Jul 01^st, 2009, 10:49pm

Hi All,

I am trying to simulate the frequency response of a switched capacitor amplifier. For this, I have replaced the dynamic CMFB of the opamp by an ideal continuous-time one and I have frozen the clocks to amplification mode (that is, now the amplifier has the capacitive divider feedback around the opmap). And I am biasing the input nodes of the opamp to the right common mode through BIG inductors.

With this configuration, if I run .OP, the simulation shows convergence error. I need some help to fix this. Is there any fundamental issue with respect to such a setup to characterize the switched-capacitor circuits?

Thanks & Regards
Rajesh

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buddypoor

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Bremen, Germany

Re: AC response & step response simulation of a switched-capacitor amplifier
Reply #1 - Jul 2^nd, 2009, 5:08am

rajeee1000 wrote on Jul 1^st, 2009, 10:49pm:

............ and I have frozen the clocks to amplification mode (that is, now the amplifier has the capacitive divider feedback around the opmap). ............

Rajesh

I�m afraid this cannot work since - for my opinion - there is no "amplification mode". You cannot use only one "frozen" switch configuration and expect at the same time a reasonable behaviour of the opamp.
Instead you have to apply the classical ways for ac simulation of S/C circuits : Specific s/c oriented simulation routines as e.g. in spectre or replacement of all s/c blocks with corresponding time continuous linear blocks.

Regards

LvW (buddypoor: In memory of the great late Buddy Rich)

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