Ultralow-Power Class-C Complementary Colpitts Crystal Oscillator

This letter presents a 24-MHz ultralow-power and lowphase-noise complementary Colpitts crystal oscillator. Class-C operation is realized by biasing the oscillator always in the weak-inversion region with the proposed circuit. A Langasite-type CTGS (Ca
₃
TaGa
₃
Si
₂
O
₁₄
) crystal resonator, with the characteristics different from those of quartz (SiO
₂
), helps to reduce the startup time to less than 1 ms. An injected gm-booster is implemented to speed up the oscillation further. Prototype chips in 65-nm CMOS were evaluated with CTGS and quartz resonators. With each type, the lowest steady-state power consumption and the best jitter FoM have been achieved. With the CTGS resonator, the startup energy as low as 10 nJ has also been achieved.