OPA2652: OFFSET at Input Pins and Unexpected Output

Hello Prajwal,

Your high-pass filter implemented with the 3.2nF capacitor and 1MOhm resistor are causing the offset.  If you try a 1.6uF capacitor and 2kOhm resistor, you will see very little offset and normal operation.  Because of the large resistor to GND, the amplifier inputs handle a distorted signal, affecting the feedback network and resulting Vout signal.

If you try 640uF and 5kOhm resistor, you will see a smaller offset compared to 3.2nF and 1MOhm.  Please try your own resistor and capacitor combinations to generate a resulting signal you are comfortable with for your application.

My circuit simulations were tested with 15 Ohm heavy load, 100 Ohm load, and 1kOhm (datasheet and reference design default) load.

I would suggest selecting capacitor values between 32nF and 2uF, and selected resistor values between 100kOhms and 1kOhm.

You can fix the behavior you are observing by addressing the high-pass filter at the op-amp input.  You may also consider using the second amplifier channel as an active high pass filter: https://www.electronics-tutorials.ws/filter/filter_6.html

For either passive or active HPF, you should change your capacitor and resistor values.  

Best,

Alec