A 32kHz crystal oscillator leveraging voltage scaling in an ultra-low power 40nA real-time clock

In this paper, an ultra-low power consumption crystal oscillator embedded in an RTC module (ASIC and its crystal resonator) is presented. The technique leverages oscillation amplitude and loads capacitance scaling; it incorporates transistor level merging and a power injection mechanism in the resonator to reduce power consumption. The crystal oscillator starts up without additional complex circuitry. Measured power consumption is 10nW at 1V and operation is demonstrated from 0.6V to 5V under a regulator, while room temperature ranges from -40 to 85 degrees C across four corner wafers.