A Low-Voltage Mobility-Based Frequency Reference for Crystal-Less ULP Radios

The design of a 100 kHz frequency reference based on the electron mobility in a MOS transistor is presented. The proposed low-voltage low-power circuit requires no off-chip components, making it suitable for application in wireless sensor networks (WSN). After a single-point calibration, the spread of its output frequency is less than 1.1% (3σ) over the temperature range from-22\,∘Cto 85\,∘C. Fabricated in a baseline 65$~$nm CMOS technology, the frequency reference circuit occupies 0.11\ mm²and draws 34 a 1.2 V supply at room temperature.