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offset of fully differential amplifier

 
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manissri



Joined: 16 Apr 2005
Posts: 267
Helped: 6
Post08 May 2008 20:21   offset of fully differential amplifier
how to measure the offset of fully differential amplifier.
any test bench doc or pdf available would be appreciable.
regards
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jecyhale



Joined: 19 Feb 2008
Posts: 402
Helped: 39
Location: China
Post09 May 2008 5:50   Re: offset of fully differential amplifier
Is offset very improment for differential amplifier?
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spring1860



Joined: 02 Nov 2007
Posts: 94
Helped: 3
Post09 May 2008 6:15   Re: offset of fully differential amplifier
hi
see the following connection, and the out will be the offset

hope it helped to you.

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manissri



Joined: 16 Apr 2005
Posts: 267
Helped: 6
Post09 May 2008 9:56   Re: offset of fully differential amplifier
HI Spring thanz for reply.
can u tell me what wud be the value of resistance which has connected into the feedfback and how it will measure the offset of the amp.
regards
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lvlei0309



Joined: 29 Apr 2008
Posts: 24
Helped: 2
Post09 May 2008 11:11   Re: offset of fully differential amplifier
Connect the OPAMP with buffer structure, can simulate the offset volt. Use montecalo analysis can track the change of offset volt.
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spring1860



Joined: 02 Nov 2007
Posts: 94
Helped: 3
Post10 May 2008 16:38   Re: offset of fully differential amplifier
manissri wrote:
HI Spring thanz for reply.
can u tell me what wud be the value of resistance which has connected into the feedfback and how it will measure the offset of the amp.
regards


hi
r1=r3,r2=r4. RL and CL is the load of your circuit. CMFB must work.
do OP analysis and the difference between VON and VOP ( VON - VOP)is the offset of total ckt. then , r1/(r1+r2)*(VON-VOP) will be the offset of the amp.
B.R.
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kwkam



Joined: 25 Feb 2002
Posts: 281
Helped: 11
Location: Somewhere on earth
Post10 May 2008 18:29   offset of fully differential amplifier
To measure the differential amplifier's offset. You can use R2=R4=0 and remove the R1 & R4. Then measure the voltage different between Von & Vop
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udintbr



Joined: 15 May 2008
Posts: 5
Post15 May 2008 15:21   offset of fully differential amplifier
What is Vcom (the 3rd input of amp)? If my Vdd=2.5, so my Vcom = 1.25V?
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BackerShu



Joined: 22 Dec 2007
Posts: 26
Post16 May 2008 14:56   Re: offset of fully differential amplifier
udintbr wrote:
What is Vcom (the 3rd input of amp)? If my Vdd=2.5, so my Vcom = 1.25V?

Sometimes it is! In fact, Vcom is the voltage that the op can work well base on it. And the value of Vcom is in a certain range. Vdd/2 is usually a suitable value, but isn't the only choice.
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manissri



Joined: 16 Apr 2005
Posts: 267
Helped: 6
Post02 Jun 2008 20:03   Re: offset of fully differential amplifier
i fully agree with the above discussion that we if put the diff amp into the buffer configuration and put the vcm (common mode voltage) at the both input of amp the diff bet the both output is the offset of diff amp
but the issue arises :
if we put the diff amp into the buffer mode the gain error will also come at the output ---> is it?
coz the gain error wud be 1-(1/A) where A is the open loop gain of diffamp
so the offset we are measuring is the correct offset.
please clarify this
regards
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