I have a circuit that measure the 50Hz AC voltage and current through potential divider and shunt resistor respectively. It do that through inverting amplifier using OPAMPs. It has some DC blocking capacitors and DC biasing in the positive input of the OPAMP as seen in the picture below.
I have made a polygon cutout (The polygon is in the bottom layer) under the inverting input of the differential amplifier as suggested by TI OPAMP for everyone design note.
Still I have a 50Hz capacitive coupled noise of 32mV in the output of the opamp. And I would like to make it smaller.
Another thing to add is when performing the fast transient bursts test of 2.5 KHz 4kV. The noise coupled has very large peaks that affect the measure circuit. Although I have a MOV 20D471K in the input of the circuit. The layout is shown in the picture below.
So if the layout is poor?
Or I have to reduce the resistance further more?
Or there is another suggestion?