Op-amp: amplifying DC bias problem in output?

Question

I'm trying to do a simple 1 kHz, 1 V p-p sine wave amplification circuit using a TL071 or similar op-amp. The simulation is currently in LTSpice.

I've biased the VCC to half to try to achieve a good voltage swing but the waveform clips; it seems that the op-amp is amplifying my DC bias also.

I don't expect this op-amp to be rail-to-rail, of course.

First, here are the output waveforms:

V(out) is the small output signal, red is the AC sine wave, green is the biased waveform, centered at VCC/2.

Here's my circuit:

Any help? I'm new to this world of op-amps and struggling a bit.

Answer 1

The 'ground' on R3 becomes the 'zero reference' for the amplification. This should be connected to Vcc/2. Otherwise you will get strange results (what you are seeing).

There is some good information here about how to generate a virtual ground for this type of single-supply circuit: http://tangentsoft.net/elec/vgrounds.html