A 5.02nW 32-kHz Self-Reference Power Gating XO With Fast Startup Time Assisted by Negative Resistance and Initial Noise Boosters

We present a 32.768 kHz crystal oscillator with ultra-low power operation and a fast startup featuring for IoT applications. A self-reference power gating scheme detects the amplitude of a clock, enabling a negative resistance booster to awake XO and keep the oscillation with a duty-cycling technique for minimizing power consumption. In addition, a relaxation oscillator injects in-band noise initially, further reducing the startup time. The prototype XO for proof-of-concept was fabricated in 0.11- \mu \text{m} CMOS and fully characterized. It consumes 5.02 nW at 0.5-V supply and achieves the startup time of 1.26 s simultaneously.