Designer’s Guide Community

pipeline Junior Member Offline Posts: 10	How to sim opamp's input referred system offset? Sep 13^th, 2007, 9:32am Could system offset be determined by simulation? Or just by analysis and hand calculation? Is Monte-Carlo simulation only suitable for random offset? :-/I'm confused about these questions. Would any one kindly elaborate them? Thanks very much.
Back to top	learning to walk on the road of analog IP Logged

Berti

Community Fellow

Offline

Posts: 356

Re: How to sim opamp's input referred system offse
Reply #1 - Sep 13^th, 2007, 10:39pm

Systematic offset is caused either by asymmetrical circuits or layout. It is therefore
straight-forward to simulate systematic offset with a circuit simulator(using post-layout
back-annotation, respectively).
For random offset you can use monte-carlo simulation assuming your design-kit provides
you with statistical data.

To simulate offset you should therefore add asymmetrics from the layout into your
schematic (at least parasitics, PWE and STI is only required for 130nm and below)
and run a monte-carlo simulation using the statistical data provided by the fab.

Regards

Back to top

IP Logged

pipeline Junior Member Offline Posts: 10	Re: How to sim opamp's input referred system offset? Reply #2 - Jun 20^th, 2009, 8:24pm Clear! Thank you very much!
Back to top	learning to walk on the road of analog IP Logged

raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: How to sim opamp's input referred system offset? Reply #3 - Jun 21^st, 2009, 12:53am hi berti, i have one doubt in systematic offset, lets say i have an opamp with output biased at 1v and assume now i have connected opamp in unity gain configuration and gave .7 as input, so now offset is .3/(open loop gain) ..is this systematic offset? Thanks, Rajasekhar.
Back to top	IP Logged

HdrChopper

Community Fellow

Offline

Posts: 493

Re: How to sim opamp's input referred system offset?
Reply #4 - Jun 22^nd, 2009, 9:36am

raja.cedt wrote on Jun 21^st, 2009, 12:53am:

hi berti,
� �i have one doubt in systematic offset, lets say i have an opamp with output biased at 1v and assume now i have connected opamp in unity gain configuration and gave .7 as input, so now offset is .3/(open loop gain) ..is this systematic offset?

Hi Rajasekhar,

That is not a realistic scenario: since the opamp is in closed loop, the input referred offset is equal to the ouput offset / closed loop gain; assuming sufficiently large open loop gain. Therefore 0.7v input referred offset means 0.7v output referred offset, although obviously .
these are not realistic offset magnitudes.

Regards
Tosei

Back to top

Keep it simple

IP Logged

aaron_do Senior Fellow Offline Posts: 1398	Re: How to sim opamp's input referred system offset? Reply #5 - Jun 24^th, 2009, 6:03pm Hi Raja, if you have an op-amp in unity gain configuration, the output should follow the input. So how do you "bias" the output at 1V? cheers, Aaron
Back to top	there is no energy in matter other than that received from the environment - Nikola Tesla IP Logged