6.3 A 45.5μW 15fps always-on CMOS image sensor for mobile and wearable devices

Most mobile devices embed a CMOS image sensor (CIS) for capturing images. In addition, a variety of sensors such as proximity, ambient light, and fingerprint sensors are integrated for device control. The integration of multiple sensors in a device requires significant power consumption, area, and cost. In contrast to multiple sensors, an always-on CIS enables advanced smart sensing, including gesture sensing, face recognition, eye tracking, and so on. Smart sensing using a CIS offers a variety of user interfaces and experiences such as touch-less control, authentication, gaming, and object recognition for the Internet of Things (IOT). A major drawback of a CIS in mobile devices is that it consumes power greater than 50mW [1], and this is not feasible for always-on sensing that is required to function with the limited energy available from the device's battery. Moreover, power reduction in a CIS causes image degradation owing to reduced SNR, which is not acceptable for capturing high-quality images. Many low-power CISs have been reported [2-3]. However, they are inadequate for use as high-resolution sensors because of the requirement of additional in-pixel circuits for device operation at low supply voltages.