A crystal-less bluetooth low energy radio using a MEMS-based frequency reference system

A system clock is implemented with a 2.52 GHz MEMS-based oscillator, divider, temperature sensor, digital PLL, and active temperature compensation to generate a 48 MHz frequency reference with ±10 ppm stability from −40°C to 105°C. An on-chip 32 kHz RC oscillator is also periodically calibrated by this reference clock to achieve ±500 ppm accuracy, allowing it to be used as the wireless node sleep timer. Additionally, the MEMS oscillator is advantaged in highly duty cycled protocols due to its 100x faster start-up time. This fully integrated reference system enables a crystal-less Bluetooth Low Energy compliant radio in 65 nm CMOS and could provide on-board design convenience to end users.