Photoconductor receiver sensitivity

The various contributions to photoconductor (PC's) noise are calculated and are used to determine the sensitivity of digital photoconductor receivers for use in lightwave communication systems. We find that Johnson noise is the most significant source of noise current up to bit rates as high as 4 Gbit/s, above which FET channel noise becomes dominant. In comparing the results obtained for ideal photoconductive receivers with receivers employing p-i-n photodetectors, we find that the sensitivities of both circuits are comparable, provided that low-capacitance p-i-n receivers are employed. In contrast, we find that avalanche photodiode receivers have higher sensitivities than either photoconductor or p-i-n receivers over the entire bit-rate range considered. It is concluded that equalization necessary for photoconductor receiver operation at high bit rates due to a limited gain-bandwidth product significantly degrades the sensitivity of the receiver.