Hi everyone,
I am using OPA855 as a trans-impedance amplifier with the photoelectric conversion. But it bothers me a lot that the output of the trans-impedance amplifier has a DC bias. The schematic diagram isattached below. The details of the problem are as follows.
1. In order to eliminate the influence of dark current, I removed the APD and just connected the amplifier input (left end of R60) to GND. There is several mV bias at the ouput of U15. After the second (U16) and third (U17) stage of amplification, the bias can increased to several hundreds mV. Why the first trans-impedance stage has such a bias? Is my schematic diagram incorrect?
2. My amplifiers are powered by ±2.5V. But there is 50 mV difference between the postive voltage and the negative voltage. Does it matter?
3. Will the input impedance of the inverting and noninverting input of OPA855 influence the output bias? Is the input impedance of the inverting same to the noninverting input?
4. The circuit has oscillation at some frequencies. Is there any effective way to eliminate the oscillation?
Many thanks
Zhao