A 1.4-mW 14-MHz MEMS Oscillator Based on a Differential Adjustable-Bandwidth Transimpedance Amplifier and Piezoelectric Disk Resonator

Abstract

This paper presents an oscillator based on a fully differential adjustable-bandwidth transimpedance amplifier (TIA) and a piezoelectric micromachined bulk-mode disk resonator. The TIA includes a regulated cascode stage and a common source active feedback topology. The TIA is designed in 65-nm CMOS and consumes 1.4 mA from a 1-V supply. The measured maximum mid-band transimpedance gain is ~80 dB $\boldsymbol {\Omega }$ and the TIA features an adjustable bandwidth of up to 214 MHz, when driving a shunt parasitic capacitance $C_{P}$ of 4 pF. The measured input-referred current noise of the TIA at mid-band (i.e., ~20 kHz–40 MHz) is below 3.7 pA/ $\boldsymbol {\sqrt {\text {Hz}}}$ . The TIA is connected with the disk resonator in [1] , and the oscillator performance in terms of phase noise and frequency stability is reported. The measured phase noise in air and under vacuum, at a 1-kHz offset, is −104 and −116 dBc/Hz, respectively. The close-to-carrier phase noise is also low in air and under vacuum with −40 and −60 dBc/Hz, respectively, at a 10-Hz offset, while the far-from-carrier phase noise reaches −130 dBc/Hz. The measured short-term stability of the MEMS oscillator is of ±0.38 ppm.