Experimental study and analysis of soft and permanent errors in digital cameras

Abstract

Digital cameras, like other digital circuits, experience hits by high-energy cosmic particles. In regular digital circuits, if the charge deposited by a particle hit happens to change the state of a flip-flop, the circuit will suffer a short lived error that is often called a soft error or a single event upset (SEU). If, on the other hand, the deposited charge propagates through the circuit without causing a state error, there will be no indication that such a hit ever occurred. The latter is often called a single event transient (SET). In contrast to other ICs, the CMOS Active Pixel Sensor (APS) in a digital camera can record the effect of most particle hits by displaying a pixel output that is brighter than the incoming illumination. Although in regular ICs particle hits rarely cause permanent damage, permanent defects in digital camera pixels, caused by cosmic particles, are very often observed in practice. This paper presents an experimental study of SEUs in digital cameras and compares their rate to that of SEUs in SRAM memory and to the rate of permanent defects in cameras. The analysis of SEUs in digital cameras can provide important information about the nature and distribution of particle hits and their occurrence rate, about the development of permanent defective pixels (also called “hot pixels”), and increase our understanding of SEUs in regular ICs.