Analysis, modeling and implementation of a new 1.8V fierce-gate crystal oscillator based on the constant cell in 28nm CMOS technology for automotive radar applications

Abstract

The majority of analog and digital integrated circuits with built in crystal oscillator use the Gated Pierce design where the oscillator is built around a single CMOS inverting gate. In most applications that require a high level of precision and stability of the performances versus Process, Voltage and Temperature (PVT) variations, this design is not suitable. The inverter cell itself is very sensitive to PVT variations, negatively affecting the overall performances of a crystal oscillator. This paper shows a new Pierce-Gate crystal oscillator based on the constant gm cell, implemented in 28nm CMOS TSMC technology. The oscillator can work with any crystal frequency between 20 MHz and 100 MHz, the power supply is 1.8V and the output is a 50% duty cycle square waveform. Simulations and measurements show that the new designed crystal oscillator is superior in terms of phase noise performances (−123 dBc/Hz at 100 Hz offset at 60 MHz and −163 dBc/Hz at 1MHz offset at 60 MHz), phase noise variation over PVT, Power Supply Rejection Ratio (PSRR), output frequency and output duty cycle stability, and input impedance with respect to the state of the art counterparts. The implemented crystal oscillator is very challenging and suitable for automotive radar applications.