**7. Companion electronic circuitry**

A block diagram of this circuitry is depicted in Fig. 7. All photodetector p-n diodes in the array of FPPD under the channel produce a current whose magnitude contains information related to light intensity. Furthermore this light intensity, which is absorbed by the photodiodes, depends on the content of the chemicals present in the micro-channel fluid. The main purpose of this electronic circuitry is to collect, condition, and interface these current signals to the post processing circuit. Since the information signals are in the form of diode currents, it is preferred to work with current mode (CM) electronic circuits.

Fig. 7. Companion Electronic circuit connects array of FPPD to the microprocessor
