17.7 A 1.89nW/0.15V self-charged XO for real-time clock generation

A 32.768kHz crystal (XTAL) with its oscillation circuit is widely adopted for the generation of the real-time keeping and system-standby clock. Both functions are universally demanded by various systems such as cellular phones, smart wearable devices, GPS, etc. High frequency stability against environmental variations is necessary to meet system requirements. To increase the system stand-by time under limited battery capacity, an ultra-low power crystal oscillator (XO) is strongly demanded.

[1]  W. Thommen,et al.  An improved low power crystal oscillator , 1999, Proceedings of the 25th European Solid-State Circuits Conference.

[2]  D. Aebischer,et al.  A microprocessor-based analog wristwatch chip with 3 seconds/year accuracy , 1994, Proceedings of IEEE International Solid-State Circuits Conference - ISSCC '94.

[3]  David Blaauw,et al.  A 5.58nW 32.768kHz DLL-assisted XO for real-time clocks in wireless sensing applications , 2012, 2012 IEEE International Solid-State Circuits Conference.

[4]  D. Ruffieux.  A high-stability, ultra-low-power quartz differential oscillator circuit for demanding radio applications , 2002, Proceedings of the 28th European Solid-State Circuits Conference.