A low-power sensor processor with a approximation-based fractional wakeup timer for long-term sleep of wearable sensor devices

The proposed chip is an ultra low-power sensor processor specifically designed for deep-sleep synchronization of wearable glasses to realize 3DTV vision effect, which can be widely applied for traditional IoT sensor devices using long-term sleep operations. This proposal implements a newly designed fractional-order synchronizer by adjusting the synchronization accuracy of the stereovision without external sync information using a heavy RF-baseband chip. The fractional-order synchronizer enables accurate synchronization based on the approximation method of the fractional residue regardless of sync-clock speed and allows the input wireless sensor to be turned off to provide perfect flicker-free synchronization in deep-sleep operating mode. The implemented one-chip solution uses less than roughly 11%(10x) of the operating current that major commercial shutter glasses use. While the input wireless sensor is off, the internal synchronization experiences only a 1.5% deviation in the sync timing over the running time of a two-hour movie. This enables a perfect flicker-free feature without any interruption in the synchronization of stereovision and reduces the operating current by the perfect synchronization in deep-sleep mode. This paper describes the system architecture, including the details of the proposed techniques and identifies the system key concepts and functions.