A ±10ppm −40 to 125°C BAW-based frequency reference system for crystal-less wireless sensor nodes

A frequency reference system is implemented with a BAW-based 2.52GHz oscillator, divider, temperature sensor, digital PLL, and final test at three temperatures to create a 48MHz reference frequency with +/-10ppm stability from -40 to 125°C. This reference clock periodically recalibrates a fully integrated 32kHz RC oscillator to less than +/-500ppm frequency variation so that it can be used as the wireless node sleep timer. The reference system enables a Bluetooth Low Energy compliant radio in 65nm CMOS to be realized without any crystals.