More on: TI’s on-chip bulk acoustic wave oscillator to replace external crystals

Texas Instruments has removed the need for external timing crystals by developing a technique for building high-grade thin film piezoelectric bulk acoustic wave (BAW) resonators within the metallisation of silicon chips, on a CMOS-compatible process that can be delivered in a standard, or even thin, QFN package.

The crucial piezo film is sandwiched between two metal electrodes and several acoustic reflectors to confine mechanical energy (see diagram). “The end result is a very stable high-Q resonator tank,” said the firm, which is claiming a Q of ~1,200 for its ‘VCBO’ (voltage-controlled BAW oscillator), leading to low jitter (see below) and frequency stability of +/-40ppm across temperature, voltage and aging. High vibration and shock resistance is also claimed.

Update: Electronics Weekly asked of TI: ‘Is the oscillator is inherently aging-proof, or is aging compensation is applied’, to which TI replied: “Aging compensation is applied via the radio sub-system core [see application below], this is fully transparent to the user.”

TI is not intending sell simple quartz-replacing oscillator chips based on its BAW technology, but rather use the resonators in devices that extend existing product lines.

Its first two BAW-containing chips will be the CC2652RB wireless microcontroller and LMK05318 network synchroniser clock.

The above figures come from the LMK05318 frequency synthesiser, which includes jitter smoothing locked loops. To those figures, TI adds: “2.5GHz VCBO 1kHz-100kHz phase noise [red left] is about 10-20dB better than the state-of-the-art LC VCO [its own LMX2582 synthesiser, black left], which demonstrates the phase noise/jitter advantage of VCBO. The typical total rms jitter is 33fs at 1250MHz output, and is 47fs for 312.5Mhz output. The output clock maximum total rms jitter is less than 100fs, exceeding specification required for 400Gbit/s communication networks.”

CC2652RB, available in 7 x 7mm VQFN (very thin QFN), uses its resonator to replace an external 48MHz crystal. It is a multi-protocol 2.4GHz wireless microcontroller that can implement Zigbee, Thread, Bluetooth low energy and proprietary protocols. It can operate over -40°C to 85°C.
The SimpleLink CC2652RB wireless MCU-based TI LaunchPad development kit is available

LMK05318, 7 x 7mm 48pin VQFN, is a single-channel network synchroniser clock is aimed at 400Gbit/s and is claimed to “deliver the lowest bit errors for 56Gbit/s and emerging 112Gbit/s pulse-amplitude modulation-4 links,” according to the firm. Another claim is “industry’s best hitless switching performance” – at +/- 50ps phase transient.
LMK05318 evaluation module is available.