2021 Volume 18 Issue 16 Pages 20210275
This paper presents an ultra-low power 32.768 kHz crystal oscillator circuit for the real-time clock (RTC) generation. A negative feedback amplitude control loop is employed to reduce the oscillation amplitude and the energy loss of the crystal. To further reduce power consumption, the inverting amplifier is powered on periodically by a duty-cycling control pulse, which reduces the static power of the amplifier significantly. Trading off among power consumption, area and design complexity for generating a precise duty cycle pulse, the output square wave of the crystal oscillator circuit is used as the control pulse. The circuit is designed in 55-nm CMOS process with an area of 0.04mm2. It shows a power consumption of 8.83nW which cuts the power consumption by 37% comparing with the circuit without pulse control. The proposed circuit achieves a great temperature stability of 0.14ppm/℃ from -40℃ to 100℃ and a power supply sensitivity of 30.5ppm/V over supply voltage of 0.5-0.8V.
