Utilization of Programmable I/O of RP2350 Microcontroller With CMOS SPAD Sensors

Abstract

A large amount of data produced by single-photon avalanche diode (SPAD) arrays is a well-known challenge, which is commonly resolved with a high-speed custom interface on a field-programmable gate array (FPGA). In this letter, we present a custom interface utilizing programmable I/O blocks of Raspberry Pi RP2350 microcontroller and show that RP2350 can replace FPGAs in some use cases. Only one of the three programmable I/O blocks on RP2350 and about 40 lines of assembly code were enough to handle 21 time-deterministic signals between RP2350 microcontroller and an optical transceiver. Most importantly, the implemented interface achieves data transfer from the transceiver to RP2350 at 900 Mb/s without loading the main processor of RP2350. The operation of the interface was demonstrated by measuring a photoplethysmogram from a fingertip at 500 Hz sample rate. During the measurement, the power consumption of RP2350 was 110 mW, which was less than a third of the system's total power consumption.