I have a significant DC offset at the out of the circuit.
Could anyone explain the reason for this ...
The offset is caused by R1 (50k). If you will look on the specifications table of the datasheet, you will see that the Input Bias Current of AD8021 is at a typical value of 7.5 uA (+ 5V supply). So, 50 kohms*7.5 uA = 375 mV. And this is the value of the offset that you will see on the output. To get rid of this, please lower the values of the resistors. Figure 2 shows suggested values for each gain configurations.
Also, please note that the coupling cap, C1, will form a high pass filter in combination of Rin. Make sure that the combination should not deteriorate your signal prior to the amplifier.
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