Hi there, I'm measuring the voltage on the output of an amplified photodiode circuit that is capturing light emitted by an Liquid Crystal Display (LCD) projector and there is a periodic voltage drop which I don't know the reason. The projector is projecting an all-white image. I've been reading that LCD displays must be AC powered because if they are powered using DC there will be electrochemical reactions that will make them to fail. I can see the AC modulation on the signal and that is ok for me. What I cannot explain is the origin of the periodic voltage drop/ripple. As an attachment you can see the plot of this signal. Any help would be greatly appreciated. Thank you very much in advance!