Chapter 5: 3 Sources of Noise

  1. Signal Short Noise

Definition

Quantum noise arising from discrete nature of incident signal

Photon absorption is discrete process. Thus, number of absorption fluctuates statistically.

Mean square noise current Signal Short Noise

  1. Dark Current Shot Noise

Definition

Arising from discrete nature of incident nature of photodiode dark current

Dark current, Id

Current with no incident light

Bulk dark current, Ib + surface leakage current, Ii

Mean square DCSN Dark current noise

Thermal noise

Arises from random thermal motion of carries in resistive circuits element

Mean square thermal currrent noise
Thermal noise

Fluctuation due to random motion of electrons

Signal noise ratio (SNR)

Definition

Ratio of signal current squared to total mean square noise current

Total mean square noise current snr 1

SNR formula snr 2

SNR for an APD

Gain factor of M apd