DC Bias and Op Amp

simulate this circuit – Schematic created using CircuitLab

I want to add a DC volatage of 1.25V to a sine wave signal. I am using a DC bias circuit with a voltage divider (R1=R2=100Kohm) connected to a 2.5V source and to the ground. That is giving me the correct 1.25V DC offset that I need in my application.

However I would like to lower the impedance so I am using a voltage follower op amp. I am using the LT6202 op amp which is supposed to be rail-to-rail and unity gain stable. When I connect the voltage follower to the DC bias circuit I mentioned above, the DC offset rises from 1.25V to 1.32V.I have done the simulation also and I am getting the same results.

When I am using R1=R2=10KOhm instead of 100KOhm the DC offset becomes 1.258V, which is closer to the wanted 1.25V value.

I am not sure what is causing that. Any help?

• You need to show us your schematic if we're to have any hope of helping you. Nov 11 '15 at 14:23
• Where are you measuring the offset? At the input or the output? Nov 11 '15 at 14:37
• The offset is measured both in the input off the op amp and at the output and is for both around 1.236V with a real small flactuation between those two points.
– JPa
Nov 11 '15 at 14:41
• Where's your input signal in the schematic? You say it's 1.23V, which is very close to the desired 1.25V, but don't mention that in your question - which figure is correct? Nov 11 '15 at 14:44
• I do not have an input signal on that schematic, I am trying to understand at the moment why I am not getting the expected 1.25V from the above circuit but I am getting a 1.32V DC offset instead. The input signal will be connected at the C1 at the side that is currently connected to the ground.
– JPa
Nov 11 '15 at 14:47