This topic presents a 16-MHz digital-controlled crystal oscillator and a time-domain temperature sensor design to achieve a high-precision auto calibration temperature-compensated crystal oscillator in a low-power mobile device. The digital-controlled crystal oscillator is based on Pierce readout topology with two 8-bit switched-capacitor arrays. The temperature is measured with the temperature-dependent delays of the proposed delay cell, called time-domain temperature sensor. The supply voltage 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 designed circuit has been successfully fabricated by using TSMC 0.18-μm CMOS process, where the active area is 2.2 mm2. The measured phase noise of 1 kHz offset at 25C is -116.37 dB/Hz. The frequency deviation over -40˚C to 85˚C is within +/- 0.2 ppm after compensation. The measured effective temperature resolution of the time-domain temperature sensor is 0.18˚C/LSB and the measured error is within -2˚C to 1.6˚C at 1k Hz conversion rate. The measured current consumption of the chip is about 2.5 mA.
Keywords: Crystal oscillator, Digital control, Temperature compensation, Low power, Delay cell, Temperature sensor.