(An) analog-digital hybrid CNN face recognition processor for always-on mobile devices

Abstract

An ultra-low power analog-digital hybrid always-on face recognition (FR) processor integrated with a CMOS image sensor (CIS) is proposed for the wearable mobile devices applications such as user authentication. The proposed processor is the first IC with full process of FR in a single chip. The processor adopts analog-digital hybrid convolution operation for efficient integration of CNN processor with CIS. The analog convolution processor is proposed for the computation of the $1^st$ layer of CNN and the quantization operation without an ADC that can achieve 15.7% power reduction with 1.37% minimal accuracy loss. In addition, the analog weighted-sum unit with low power ($< 20\muW$) and high efficiency (> 5.18TOPS/W) is proposed with switched-drain regulation (SDR) current mirror which can achieve less than 6% mirroring error. The processor is simulated in 65-nm CMOS technology, $15.84mm^2$ area with 2.5V and 1.2V for analog domain and 0.77-1.1V for digital domain. It consumes 0.141mW to evaluate one face at 1 fps and achieves 96.18% FR accuracy in LFW dataset.