This amplifier I'm working on is designed to work with small signals, less than 10mV. The TLO82 chip is being powered with ±10v. The problem I have is DC offset in the output. What an AC signal input, the output is only being driven positive, no part of the waveform crosses ground.
With gain at 38db, the offset is 0.4 volts. The voltage of the output signal (DC component removed) is 0.4 volts. The signal and offset aren't constantly the same, as at 44db, the offset is 1 volt and signal is 0.8 volts. Input is 1khz, 5mV. Offset seems constant regardless of frequency.
I can get a proper AC signal out only if I set the offset of the input signal to -5mV. This value doesn't change no matter what the input level is.
Basically, the op-amp is acing like the input is offset 5mV positive when it's not, and the only way to counter it is to set the offset negative. What's going on here?
This is the relevant part of my schematic:
With gain at 38db, the offset is 0.4 volts. The voltage of the output signal (DC component removed) is 0.4 volts. The signal and offset aren't constantly the same, as at 44db, the offset is 1 volt and signal is 0.8 volts. Input is 1khz, 5mV. Offset seems constant regardless of frequency.
I can get a proper AC signal out only if I set the offset of the input signal to -5mV. This value doesn't change no matter what the input level is.
Basically, the op-amp is acing like the input is offset 5mV positive when it's not, and the only way to counter it is to set the offset negative. What's going on here?
This is the relevant part of my schematic: