A method for monitoring a circuit. The method may include obtaining, using a total current monitoring device, a measurement of a current transmitted through a cathode in a photodetector circuit. The current may include a first photocurrent for a first photodetector and a second photocurrent for a second photodetector. The method may include obtaining, using a differential current monitoring device in a transimpedance amplifier circuit, a differential voltage proportional to a current difference between the first photocurrent and the second photocurrent. The transimpedance amplifier circuit may generate, using the first photocurrent and the second photocurrent, a first output signal and a second output signal. The method may include determining, using the differential voltage and the measurement of the current transmitted through the cathode, an amount of the first photocurrent and an amount of the second photocurrent.