I have been experimenting with an opamp as a noninverting amplifier for a Piezoelectric vibration sensor 0-1Khz expected. I am only interested in the positive portion of the signal as an average hence the big Cap on the output signal. My problem is bias voltage injection. When the gain network is tied to the ground the circuit works as expected. but I have since tried to inject a 0.5v bias voltage via a divider network but I'm not getting the response expected.
I suspect it's the divider network because it's in the same order of magnitude as the gain network but I don't have larger values to test at the moment so I hope someone can shed some light on the issue. I feel like I'm missing something obvious. The circuit is supplied from a bench 3.0V supply so it's trustworthy.
The Opamp used has a 1.3mv offset and with an x101 gain, I expect to see 131mV on the output with no input signal and am currently getting 129mv so it seems accurate, when I apply a steady-state 7.5mv I get 760mV out which is also expected. but when I inject the biased voltage the output is stuck at a steady state of 35mV.
So as an update thanks to the comments from members I have found a way that seems to work to provide Bias on a Noninverting amplifier. The Bias can be driven from the same supply rail on the condition that the output is buffered. in addition, the Piezo Sensor Negative ( if that's the correct term) has to be connected to the virtual ground of the same bias feedback path and not ground. Still need to test it on real circuit but simulation seems to be accurate