A Reconfigurable 10 ns Resolution, Wide Range FPGA-Based Timing Generator for CMOS Image Sensors

CMOS image sensors are now ubiquitous across automotive, security, consumer and scientific markets. CMOS pixels, are sensitive to timing variations, thereby highlighting the need to carefully characterize their performance. In this context, reconfigurable architectures such as FPGA-based systems, offer a solid and flexible electronic platform to design the needed timing wave forms for pixel characterization. In a typical 4T pixel architecture, the transfer gate transistor is most sensitive to variations in rise/fall time edges and voltage because of the charge transfer mechanisms needed to transfer the charge from the photodiode to the floating diffusion. The ability to correctly set up the pulse’s duration and resolution is therefore crucial for precise measurement of pixel parameters. In this paper, we use a simple three-register reconfigurable architecture that modulates the pixel control signal timings. Experimental results demonstrate that by using a commercial Xilinx Zynq-7020 architecture it is possible to reach a 10 ns resolution while keeping a reconfigurable timing up to almost 43 s for precise characterization of the CMOS pixels. Such approach is particularly useful for characterizing transfer gate signals and the sensor dark current where the combination of precision and long exposure times is needed.