Abstract
This article presents a 6.89 MHz MEMS oscillator based on an ultra-low-power, low-noise, tunable gain/duty-cycle transimpedance amplifier (TIA) and a bulk Lamé-mode MEMS resonator that has a quality factor (Q) of 3.24 × 106. Self-cascoding and current-starving techniques are used in the TIA design to minimize the power consumption and tune the duty-cycle of the output signal. The TIA was designed and fabricated in TSMC 65 nm CMOS process technology. Its open-loop performance has been measured separately. It achieves a tunable gain between 107.9 dBΩ and 118.1 dBΩ while dissipating only 143 nW from a 1 V supply. The duty-cycle of the output waveform can be tuned from 23.25% to 79.03%. The TIA has been interfaced and wire bonded in a series-resonant oscillator configuration with the MEMS resonator and mounted in a small cavity standard package. The closed-loop performance of the whole oscillator has been experimentally measured. It exhibits a phase noise of −128.1 dBc/Hz and −133.7 dBc/Hz at 1 kHz and 1 MHz offsets, respectively.
Highlights
Timing and frequency reference oscillators are pivotal blocks in almost all electronic systems
To validate the fabricated design, the CMOS circuits have been tested in an openloop configuration while considering all parasitic loads to validate the transimpedance amplifier (TIA) open-loop performance
Five CMOS dies have been tested in total, and all the results are within 0.3% of the TT corner performance, which is in a good agreement with our Monte Carlo simulations
Summary
Timing and frequency reference oscillators are pivotal blocks in almost all electronic systems. MEMS-based reference oscillators have become a key alternative to those based on quartz crystal resonators to enable miniaturized systems along with high performance levels [2,3,4]. The loop sustains oscillation if the forward gain of the TIA overcomes the resonator series losses represented by RM. Transduced resonators have a higher RM in the range of tens of kΩ but are more suited for monolithic CMOS integration [5], and these devices offer a high-quality factor (Q), small size, and good stability [6,7,8,9,10,11]. Capacitive MEMS resonators require a high gain TIA to compensate for the high RM. A low phase shift near the oscillation frequency ( fo) is needed to sustain oscillation This results in the trade-off between the need for a high gain-bandwidth product and low power consumption
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