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 100× 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.