This application report details TI's BAW technology, the integration of a BAW resonator with oscillator circuitry to make a standalone oscillator, and the advantages of using a BAW oscillator over a quartz oscillator. The key advantages of the BAW oscillator over a quartz oscillator include: increased flexibility, improved temperature stability, improved jitter performance, increased power supply noise immunity, significantly better vibration stability, and significantly better shock performance.
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Quartz crystal oscillators (XOs) have dominated the timing reference market for over a century since the invention in the 1920s. These crystal oscillators have found utility in a wide range of products from low-end (real-time clock) to high-end (complex radio, GPS, and military/aero) applications. In the past few decades, mobile communication and the emerging internet-of-things (IoT) markets have driven the search for new resonator technologies that consume lower power, with smaller form factor, for ease of integration, while maintaining similar or better performances than quartz crystals. A few standalone oscillator products utilizing different types of micro-resonator technologies have been released to the consumer market in the past decade. Texas Instruments started the development of its own bulk acoustic wave (BAW) resonator technology aiming for advanced timing applications since 2012 and has released a few system products including industry’s best performance jitter cleaner (LMK05318 family) and world’s first commercialized crystal-less BLE radio (CC2652RB family) since 2018. Using the mass production experience of these devices, TI is now launching the BAW-based standalone oscillator products.
TI’s BAW resonator technology utilizes piezoelectric transduction to generate high-Q resonance at 2.5 GHz. The resonator is defined by the quadrilateral area overlaid by top and bottom electrodes. Alternating high- and low-acoustic impedance layers form acoustic mirrors beneath the resonant body to prevent acoustic energy leakage into the substrate. Furthermore, these acoustic mirrors are also placed on top of the resonator stack to protect the device from contamination and minimize energy leakage into the package materials. This unique dual-Bragg acoustic resonator (DBAR) allows efficient excitation without the need of costly vacuum cavities around the resonator. As a result, TI’s BAW resonator is immune to frequency drift caused by adsorption of surface contaminants and can be directly placed in a non-hermetic plastic package with the oscillator circuitry in standard oscillator footprints (3.2 mm × 2.5 mm and 2.5 mm × 2.0 mm).