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Design >> Analog Design >> Offset voltage cancellation
https://designers-guide.org/forum/YaBB.pl?num=1255355390

Message started by raja.cedt on Oct 12^th, 2009, 6:49am

Title: Offset voltage cancellation
Post by raja.cedt on Oct 12^th, 2009, 6:49am

hi,
while reading comparators i got the this doubt, normally for Reducing offset voltage we used to keep preamp infront of the latch and then offset cancellation to latch.Why can't we apply cancellation directly to latch? what i feel for cancellation we need to put amp in feedback while charging offset on cap, where as comparator may not be work in loop, is this correct?

Thanks,
rajasekhar.

Title: Re: Offset voltage cancellation
Post by wave on Oct 12^th, 2009, 8:20pm

How much gain does your latch have? Multi-stages are used to increase gain so you are truly offset limited. No sense correcting offset if you have a gain of only 10.

Wave

Title: Re: Offset voltage cancellation
Post by raja.cedt on Oct 12^th, 2009, 9:02pm

hi,
it's better than preamp, because comparator has -ve impedance.

thanks,
Rajasekhar.

Title: Re: Offset voltage cancellation
Post by Berti on Oct 13^th, 2009, 6:24am

Rajasekhar, there have been circuits published where offset compensation (analog and digital) is employed directly to the latch.

Wave, I don't understand the following statement. Could you please elaborate on that.

Quote:

Multi-stages are used to increase gain so you are truly offset limited. No sense correcting offset if you have a gain of only 10.

Regards

Title: Re: Offset voltage cancellation
Post by raja.cedt on Oct 13^th, 2009, 7:47am

hi,
thanks for your reply, actually i am talking in the contest of the flash converters, there people are doing all these interpolation to reduce no of preamp. If we some how do offset cancellation to latch why they are puting so many preamps?

i feel following are the reasons

1. For a latch we need to use input offset storage (due to comparators high gain it may saturate if we use output storage), so while input storage we have to put latch in feedback so i am expecting stability problems and probabaly we may endup doing frequency compensation it may slow down our comparator.

2.Generally latch offset is more than preamp, so we need to wait more time to charge that offset on a cap

Sorry for the big mail..please correct me if any thing wrong

Thanks,
Rajasekhar.