Hello,
I was simulating an amplifier circuit with OPA818. I'm using two of them with each 10 x gain to achieve 100 x amplification. My input voltage is between 0.001 V and 0.035 V. I did everything according to the data sheet of the op amp, but amplification is not 100. depends on the input voltage, amplification differs between 90 and 140. I'm using LTspice and the model of OPA818, which I downloaded from the TI product website.
This is my circuit.
Many thanks in advance.
Ali
Hello Ali,
This is not a gain amplification issue, but a voltage offset issue. The OPA818 does have a relatively low offset voltage of +/-0.35mV typical, but in comparison to your input voltage this is causing a visible error at the output of the 100x gain stage.
Thank you,
Sima
Hi Ali,
when having the OPA818 remote from the 70µR shunt you can do it this way, by using a 50R cable:
Or you mount the OPA818 close to the 70µR shunt, like this:
The 33R2 resistors at the +inputs act as a weak low pass filter in combination with the input capacitances. They also help to dampen LC resonances. Sometimes it can be worth to experiment a bit with the value of these resistors.
Kai
