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I want to create an sine wave from a uC PWM with a very low DC offset. I did some research and decided to simply make a Band-Pass filter, composed by one pole passive High Pass Filter, to filter the DC component, followed by an active 3-pole sallen key filter to make the square wave sine-ish. The result is the circuit in the figure bellow.

At the breadboard i didn't face any significant problems, i got a wave with a good sine shape and with a low dc offset(10mV), but now on the PCB i'm having a significant DC offset (100mV) at the output. I tracked the signal with oscilloscope and this DC shows up right after the HP filter, in the node between R25 and R26.

Does anyone has a hint on what is going on and how can I reduce it?

Edit: PCB layout added. I applied the cooper plan in top and bottom with ground signal. I placed several vias to avoid the ground loop.

Band Pass Filter Circuit

PCB layout

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    \$\begingroup\$ This amplifier only has 5pA of bias current and 250uV of offset, so it's not the fault of the op-amp. I suspect PCB layout, maybe your ground scheme, or possibly ESD damage to the op-amp's input. Did you measure from the output to the bottom of R24? \$\endgroup\$ – John D Feb 27 '17 at 23:32
  • \$\begingroup\$ Regarding the ESD damage, its a possibility, i will try to sort it out. I have updated the post with the layout of this part. If you have a hint i would appreciate it :) \$\endgroup\$ – Impe_dancer Feb 28 '17 at 0:01
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There doesn't seem to be anything wrong with your circuit. I would check that it has been assembled correctly. Do a check on the Gerbers to make sure the PCB does what you intended it to and also that there is not any significant contaminants on the PCB (flux remnants for example).

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Answering to my question, the problem was due to ESD damage of the amplifier as suggested by user @John D. Thank you.

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