A 5.58nW 32.768kHz DLL-assisted XO for real-time clocks in wireless sensing applications

There is a growing interest in ultra-low-power wireless microsystems [1]. Synchronization between different nodes in a wireless sensor network plays an important role in the overall node energy budget due to the high power demand of wireless communication. One synchronization approach is to employ a realtime clock (RTC) on each node, with nodes awakening periodically to communicate and re-synchronize. With recent work on ultra-low-power microsystems demonstrating average power consumption of several nW [2], there is a need for ultra-low-power timers that can synchronize communication events and serve as frequency references for radios.