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Noise due to power supply

Yong Meng Sua
Prodigy 20 points

Hi all,

I have built a transimpedance amplifier to amplify the signal from a balanced detection configuration(see below). The setup works well apart from the noise due to the power supply, the spectrum of the circuit is shown too.The peak in the spectrum shoed in the spectrum around 4Mhz will when I touch or pull the cable connecting the power supply and amplifier. Can any one advice me how to get rid of the this noise, also the photocurrent signal want want to detect and amplify is at 10Mhz.

 

Thank you

Yong Meng

  • 0
    Guru 21975 points

    Yong Meng,

    Conducted noise from the power supply should be easy to filter. Since the currents in the diodes are small, you can put resistors in series with the power supplies to the diodes with capacitors to ground. Your description of sensitivity to touch suggests that there may be other issues such as capacitive coupling of interference or grounding / shielding problems. This may require careful shielding or modifications to your grounding to eliminate. I suggest that you first try filters in series with the power supplies to see if that provides improvement. Capacitive coupling and shielding issues are very difficult for us to provide advice on because it is dependent on the physical layout of your circuit. This may require careful experiments to find a solution.

    Regards, Bruce

  • 0
    Genius 5430 points

    Yong;

    With sensitive wideband transimpedance amplifiers, there is a cardinal rule-- Never use switching power supplies unless absolutely necessary. If you do, be prepared to spend a lot of time and effort to get rid of the switching noise.