A New Small-Sized Pierce Crystal Oscillator Readout with Novel on-Chip All-Digital Temperature Sensing and Compensation

Abstract

This paper presents a 16-MHz digital-controlled crystal oscillator and a time-domain temperature sensor design to achieve a high precision temperature-compensated crystal oscillator in a low-power mobile device. The digital-controlled crystal oscillator is based on Pierce topology with two 8-bit switched-capacitor arrays and the temperature of it is measured by time-domain temperature sensor. For noise reduction, the supply voltages of digital-controlled crystal oscillator and time-domain temperature sensor are regulated at 1.2 V by using two on-chip low-dropout regulators. The proposed circuit design has been successfully fabricated by using TSMC 0.18-mu m CMOS process, where the active area is 0.516 mm(2). The measured start-up time of fabricated 8-bit digital-controlled crystal oscillator is about 0.35 ms and the measured phase noise of 1 kHz offset at 25 degrees C is -119.93 dB/Hz. With temperature compensation, the frequency deviation of it is within +/- 0.08 ppm over -40 degrees C to 85 degrees C. The measured effective temperature resolution of time-domain temperature sensor is 0.45 degrees C/LSB and the measured error is within -6.3 degrees C to 7.1 degrees C at 10 Hz conversion rate. The measured current consumption of chip is about 2 mA.