APDʹs excess noise measurements using spectral analysis (FFT)

In high energy physics, the measurement of APDʹs excess noise factor is essentially made by histogram method. Another method used mainly in telecommunication field is to measure the noise spectral density using a transresistance amplifier from which the output signal is analysed by FFT (Fast Fourier Transform). The main advantage of this spectral method is the capability to separate the different domain of the whole noise spectrum. In addition, it is easy to use and is more sensitive at low bias voltage. This method also allows one to detect the generation and recombination noises if they exist. For certain type of APDs, this method gives an opportunity to measure the primary photocurrent. We have measured the excess noise of two types of APDs with this spectral method as well as histogram method. The result by the spectral method coincides well with the histogram method.