Hi all,
I am currently developing an amplifying chain with 90dB gain because the input signal is some microvolt and the desire bandwidth is from 20kHz to 200kHz. To do this I have designed a chain of 4 sallen key with ada4898 operational amplifier.
I notice that the output signal of the amplifying chain is saturated (from -5V to 5V) when the input is shorted to ground.
I think that this noise is due to the power supply.
I use a UA78M05 to provide the +5V and a LM2663 to provide the negative voltage -5V.
In purple it is the positive voltage, in green the negative voltage and in yellow it is the output of the first stage ( gain of 30dB) when the input is grounded.
Reducing the variation by adding a capacitor is not working.
I would like to know if there is an solution to reduce this noise.
Are the power supplies not correctly chosen ?
I had the idea to use voltage reference to power the op Amp. Is it a good choice?
Thank you for your help,
Kind Regards,
Florian