I have been using LT1028 in a lot of my projects to amplify bipolar signals before digitization with a (bipolar) analog-to-digital converter. Now I need to use a 5 V unipolar ADC and am trying to figure out level shifting.
The following amplification scheme works according to simulations with LT spice
(red = op amp output, blue = sine voltage input):
but unfortunately not in real life, at least in my attempts. Here is my board layout and some DC voltages that I measured with an oscilloscope.
My question: is the circuit appropriate for the LT1028? If yes, what else could be going wrong? If not, then what is a better circuit to use?
DC potential differences:
- V+ to AGND = 4.15 V (from Li cell)
- output to AGND = 3.29 V. In theory, should be ~ 2.0 V
- VC2 to AGND = 0.128 V
Solution: see accepted answer. Below is the oscilloscope trace showing amplification of a 50 mV, 10 kHz sine wave with AD8061 op amp.