How to measure the gain&phrase of a amplifier with SC cm

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kongququ

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hspice .option node post

THe amplifier with SC cmfb need some time to reach the right operation point.

So simpliy use .AC will not get the right gain and phrase margin.

How to get the open loop gain and phrase margin of the amplfier with Switch Capcitor CMFB??

Thanks

Best regards
 

Re: How to measure the gain&phrase of a amplifier with S

Dear kongququ,
I am also doing this kind of design. The method I used is:
firstly, take off all the ac source, and do transient analysis for the amplifier, of course including the part of SC cmfb circuit. Then create it's final netlist, do simulation and output it's node list(.ic file) at the time your circuit become stable.
For example, in Hspice:
.save time=10us /*if you amplifier has already become stable at 10us*/
.option node post list
After you get the .ic file, open this file, replace the line .node by .dcvolt, And then include this .ic file as stimulus file in ac analysis, you can get the gain and phase of the amplifier.
Hope this can help you!
 

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    kongququ

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Thank you!!!
Folllow your step.
I can measure it now.

But I am still wondering. At first I use .load to load the operational information from *.ic file which contain the stable information from the .save. But I failed.

Then I use .nodeset to set the voltage, and also failed.

I search the mannual of Hspice, found those commands .load,.ic, .nodeset and .dcvolt all can initialized the noal voltages.

Only dcvolt can work properly.

Who can tell me the difference between the command .ic, .nodeset, .load and .dcvolt and when to use then. Thanks.
 

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