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Simulators >> Circuit Simulators >> How to simulate chopping amp with hspice?
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Message started by trashbox on Sep 10^th, 2008, 12:34am

Title: How to simulate chopping amp with hspice?
Post by trashbox on Sep 10^th, 2008, 12:34am

Hi all,

How to simulate chopping amplifier's ac characteristic such as frequency response, noise performance with hspice or eldo? There are many swithes in the signal path.

Thanks!
Trashbox

Title: Re: How to simulate chopping amp with hspice?
Post by Frank Wiedmann on Sep 10^th, 2008, 4:41am

No idea how to do it with Hspice or Eldo, but http://www.designers-guide.org/Analysis/sc-filters.pdf shows how to do it with SpectreRF.

Title: Re: How to simulate chopping amp with hspice?
Post by thechopper on Sep 10^th, 2008, 5:09am

In Frank's reference you will find the best way to do it is by means of a pss + pac analysis. This analysis basically consider the two different operating points of your circuit corresponding to each chopper phase. In this way you will be able to see the resulting modulated offset in the frequency domain and all the associated effects of the chopper operation.

Nevertheless a fist basic (and effective) approach to sizing your circuit from the ac requirements perspective can be perfectly done with the standard ac analysis.

Regards
Tosei

Title: Re: How to simulate chopping amp with hspice?
Post by trashbox on Sep 10^th, 2008, 7:06pm

Hi tosei and Frank,
Thank for your suggestion.

Hi tosei,
Do you agree that there is no difference about the phase margin between with and without chopping switches for an amlifier?

Regards,
Trashbox

HdrChopper wrote on Sep 10^th, 2008, 5:09am:

Title: Re: How to simulate chopping amp with hspice?
Post by Tlaloc on Sep 10^th, 2008, 8:11pm

If the network doesn't change between the two phases of the chopping switches, then the phase margin of the amp would remain the same. However, the switches will add additional resistance, which, if not sized correctly could slow the entire loop.

Title: Re: How to simulate chopping amp with hspice?
Post by thechopper on Sep 11^th, 2008, 7:29pm

I agree the PM will be the same with or without the chopper being active, if - as Tlaloc suggested - you analyze the stability for the non-chopped amplifier with the switches in place to account for their contribution to the phase response. Most of the cases such contribution is negligible.

Regards
Tosei