Op Amp Problem

[Anonymous]

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

[ETRO_SSN583 · Accepted solution]

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.

[Anonymous]

hello dana,

   

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

   

Thanks

[ETRO_SSN583]

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

       

Regards, Dana.

[Anonymous]

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

[ETRO_SSN583]

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.