I'm designing a small PCB for low-level light detection. It contains an Avalanche Photodiode (APD), the DC regulator required for proper biasing (from 5V to ~65V) and a transimpedance amplifier. My question is: should I separate the ground planes for each of these parts, or there should be no problem if I use a common ground?
Ground separation
amplifierground-planepcb-designphotodiode
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Best Answer
If you have a 5V to 65V supply especially for applying negative biasing to your APD then the biggest problem is keeping that supply "micro-volt" quiet. If you can do that I doubt one bit it will matter if the two ground planes are connected or not. Me, I'd still connect the grounds and flood them like one ground plane. The last thing you want is a stable APD supply that has common mode noise to the photodiode because you might as well have a noisy APD supply.