A new small-sized pierce crystal oscillator readout with novel on-chip all-digital temperature sensing and compensation

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-μm CMOS process, where the active area is 0.516 mm². The measured startup 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°C is -119.93 dB/Hz. With temperature compensation, the frequency deviation of it is within +/- 0.08 ppm over -40°C to 85°C. The measured effective temperature resolution of time-domain temperature sensor is 0.45 °C/LSB and the measured error is within -6.3°C to 7.1°C at 10 Hz conversion rate. The measured current consumption of chip is about 2 mA.