Design optimization of the optical receiver in transcutaneous telemetric links

This paper presents a design methodology for an optimization of the optical receiver in a neural recording system. In the transcutaneous optical telemetric link (TOTL) system, light/tissue interaction produces significant scattering of the transmitted photons. Therefore, in order to increase the transmission efficiency, it is in principle advantageous to use a photodiode with a larger size to collect more scattered photons. The photodiode size, however, is limited by the bandwidth requirement. In this paper, we derive a mathematical expression of the maximum photodiode size in the presence of constraints imposed by its bias voltage and the receiver bandwidth. A numerical example using real-world TOTL system parameters is given to demonstrate the design methodology. The trade off between transmission efficiency, noise and inter-symbol interference (ISI) in terms of the 3-dB bandwidth of the receiver is investigated. To this end, receivers with bandwidth about 4/3, 3/3, 2/3 and 1/3 of the data rate are compared with respect to the sensitivity. It was found that the receiver bandwidth of 2/3 of the data rate achieves the highest sensitivity for thin tissue (2 mm) and that a receiver bandwidth of 1/3 of the data rate is preferable for thicker tissues (5 and 8 mm).