Abstract
This article presents a comprehensive guide to codesign lithium niobate (LiNbO3) lateral overtone bulk acoustic resonators (LOBARs) and voltage-controlled oscillators (VCOs) using discrete components on a printed circuit board (PCB). The analysis focuses on understanding the oscillator-level tradeoffs between the number of locked tones, frequency stability, tuning range, power consumption, and phase noise. Moreover, this article focuses on understanding the relationship between the abovementioned specifications and the different LOBAR parameters, such as electromechanical coupling ( kt2 ), quality factor ( Q ), transducer design, and the resonator size. As a result of this study, the first voltage-controlled MEMS oscillator (VCMO) based on LiNbO3 LOBAR is demonstrated. Our LOBAR excites over 30 resonant modes in the range of 100-800 MHz with a frequency spacing of 20 MHz. The VCMO consists of an LOBAR in a closed loop with two amplification stages and a varactor-embedded tunable LC tank. By adjusting the bias voltage applied to the varactor, the tank can be tuned to change the closed-loop gain and phase responses of the oscillator so that the Barkhausen conditions are satisfied for a particular resonant mode. The tank is designed to allow the proposed VCMO to lock to any of the ten overtones ranging from 300 to 500 MHz. These ten tones are characterized by average [Formula: see text] of 2100, kt2 of 1.5%, figure of merit ( [Formula: see text]) of 31.5 enabling low phase noise, and low-power oscillators crucial for Internet of Things (IoT). Due to the high [Formula: see text] of the LiNbO3 LOBAR, the measured VCMO shows a close-in phase noise of -100 dBc/Hz at 1-kHz offset from a 300-MHz carrier and a noise floor of -153 dBc/Hz while consuming 9 mW. With further optimization, this VCMO can lead to direct radio frequency (RF) synthesis for ultralow-power transceivers in multimode IoT nodes.
Highlights
R ADIO frequency (RF) synthesizers are the heartbeat of any wireless transceiver and Internet-of-Things (IoT) transceivers are no exception
This article presents the highest number of locked tones of a single acoustic resonator with competitive phase noise and FOMOSC results, making LiNbO3 lateral overtone bulk acoustic resonators (LOBARs) voltage-controlled MEMS oscillator (VCMO) a great candidate for direct RF synthesis deployed in wireless transceivers targeting multimode IoT applications
The tuning range and power consumption can be further enhanced via implementing the active circuitry in a recent-node CMOS
Summary
R ADIO frequency (RF) synthesizers are the heartbeat of any wireless transceiver and Internet-of-Things (IoT) transceivers are no exception. Direct digital synthesizers provide fast settling time, fine frequency resolution, and small area Their high noise floor, large power consumption, and spurious nature are challenging for any battery-powered IoT transceiver. As an alternative approach to both XTALs and digital methods, direct RF synthesis based on piezoelectric acoustic/MEMS is emerging for multimode IoT systems due to its potential to deliver low power, low phase noise, and wide tuning range. This article presents the first LiNbO3 LOBAR-based VCMO exploiting multiple overtones in a single resonator This VCMO features low phase noise, low power consumption, wide tuning range, and small form factor suited for multimode IoT nodes.
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