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Very Low Noise Large Area Photodiode Amplifier

Very Low Noise Large Area Photodiode Amplifier

Large area photodiodes come with a large capacitance, typically on the order of 3000pF or larger. This capacitance to ground at the input of a transimpedance amplifier has a significant effect on the output noise of the circuit as the noise gain increases dramatically at higher frequencies. AC coupling a bootstrap JFET across the photodiode clamps the diode capacitance and also allows a controlled DC reverse bias potential to be applied to the photodiode. This can optimize the sensitivity of the photodiode to light.