A 0.45V 423nW 3.2MHz multiplying DLL with leakage-based oscillator for ultra-low-power sensor platforms

Emerging demands on ultra-low-power wireless sensor platform have presented challenges for nano-watt design of various circuit components. Clock management unit, as an essential block, is one of the most actively researched blocks. It is required to distribute various frequency ranges for energy-optimal operation, e.g., Hz for internal timer [1], kHz for global clock [2], and MHz for fast data transmission or intensive signal processing [3]. However, free-running oscillators are seriously affected by process variations and should be readjusted by post-fabrication trimming. Though a crystal gives a stable frequency, the use of multiple crystals is generally not allowed by limited form-factor and increased cost. Instead, frequency multiplication from one clean reference is more effective way for higher frequency generation. Considering high-frequency clock is only intermittently used in sensor applications, the clock multiplier should provide a fast settling when turned on as well as low-power dissipation. This paper presents a 423nW, 3.2 MHz all-digital multiplying DLL (MDLL) with a digitally controlled leakage-based oscillator (DCLO) and a fast frequency relocking scheme adaptive to the amount of frequency drift during sleep state, which is required for intermittent operation of sensor node platforms.