Low-power operation of CMOS imagers using a low voltage (around 1V or less) compatible with deep submicron logic circuits enables new imager applications, such as disposable medical cameras and autonomous wireless security cameras on a chip. Pulse width modulation (PWM) [1-2] is promising for this purpose. A PWM pixel can convert light intensity to a digital pulse width by using an in-pixel comparator with a low power-supply voltage without any degradation of signal-to-noise ratio (SNR). The benefit comes from a small jitter noise in pulse coding, which is suppressed by using a voltage gain larger than unity for the in-pixel comparator. In contrast, the source-follower used in a CMOS active pixel sensor (APS) suffers from degraded SNR due to its gain being less than unity.