how to eliminate 50 Hz Power Supply noise ?

hello dear forum,

I am trying to amplify the difference of a 100 KHz signal signal from 2 identical coils

( I am trying to build a metal dedector - when metal enters the 1st coils inner , one of the signal wil be stronger and the difference will be amplified by the OPAMP circuit - thats the idea - OPAMP is AD8065 high speed amplifier

the diferential amplifier is the standart difference amplifier circuit from every common application manual - gain is 5x )



as you can see in the osciloscope picture the white signal is the output of differential OPAMP amplifier )

the yellow signal is the AC component of the 12 VDC linear power supply powering the OPAMP

as you can notice there is a 50 Hz noise coming from power supply amplified by the OPAMP

it is about 20 mV - I dont want this noise

my question is how can I eliminate this noise from my OPAMP output

thank you

Hi,

Is it possible to use a highpass filter at the output?

after the diff. amplifier I must take the the envelope of this 100 KHz signal and amplify it again

is this posible with high pass filtering the diff. amplifier output ?

You require to know whether the noise is being picked by radiation, conducted by common mode noise, or it is plain old ripple.

Substitute the power supply with a battery bank. If the noise is gone, then the noise comes from the power supply, and you can determine what are the next steps.