op-amp (transimpedancse mode) - ADC interfacing

[Rumman89]

hey friends ,
in my project ,I interfaced op-amp's (which is in transimpedance mode ) output to ADC ,my problem is , the op-amp shows some voltage say 2 volts at first place ,, but when I connect the output to ADC's input I got some 2.6 volts ..(I checkecd it on multimeter )
why so ??
please help !!!


I am in final stages of my project
:smile:

 

[saikat36]

Can you post any diagram or pic of it. It may be more helpful for us to help you.

 

[chuckey]

Does this mean that the output voltage of your amplifier changes ? Does not sound correct to me, are you sure that you have made a wiring/design error somewhere? Have you decoded the ADCs output to see what number it is producing. If its a "digital" 2.6 then all you have to do is to feed in an offset somewhere (- 2.6V?) and with no input signal the ADC will read 0V.
Frank

 

[samson A.]

No. Offseting will not do. Some opamps are internally compensated but noy to the point of unity gain at which point they go unstable and oscillate. You wont notice the oscillation on your meter because it has low pass filter built in. the oscillation swing on your 2V. whatever voltage is there when measurement begins is being sampled. I bet the meqsured voltage is not always 2.6. Either you increase the gain of amp or add a lpf at its output. OR maybe you are using the wrong adc reference voltage for converting adc result to voltage.




I could have gotten you wrong. you mean you measured both voltage with meter. the adc input of the controller is probably not configured as input and you ve got a sort of logic contention, the controller trying to drive the pin high to 5V and the opamp trying to keep it at 2V. I think.



ALL UNDER HEAVEN