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Op Amp Problem | Cypress Semiconductor

Op Amp Problem

Summary: 5 Replies, Latest post by danaaknight on 03 Mar 2013 04:27 AM PST
Verified Answers: 1
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rteg's picture
User
8 posts

Hello,

         the output of TIA is 300 mv , i am feeding to op amp negative terminal , and Op Amp(LOW POWER) configuration is shown attached ,

but the problem , what ever be the input to Op amp i should get inverted of it, but as strange i got 4.97 v . which should not be the case, what is the reason for that , how to overcome that issue

 

Thanks

user_14586677's picture
User
7648 posts

The Opamp is latched up because you have positive fdbk around it.

 

Eliminate the fdbk path from NI to Output of ther OpAmp, double click

it, set it to a follower. Run TIA output into NI input of follower. But TIA

is itself buffered, you should not need a OpAmp follower.

 

If you need to invert the TIA output then use a PGA as an inv amp.

 

Or reverse TIA input current.

 

Regards, Dana.

rteg's picture
User
8 posts

hello dana,

 Used  Inverting PGA , this having Maximum OFFSet, which is killing the real signal

Thanks

user_14586677's picture
User
7648 posts

What is the input to the TIA ? Schematic if you have one.

 

Regards, Dana.

PSoC Rocks's picture
User
141 posts

 If you are facing Offset issue, try adding a DAC to compensate it.

user_14586677's picture
User
7648 posts

The DAC brings its own set of offset and gain problems with it,

do an end to end error analysis to see how this substantively this

will not work.

 

A classic method of getting rid of offset is to use a S/H to capture the

offset, and subtract it out.

 

Another very effective method is correlated double sampling -

 

http://www.cypress.com/?rID=49159

 

Regards, Dana.

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