A Temperature Compensated RF LC Clock Generator with ±50-ppm Frequency Accuracy From-40 °c to 80 °c

This article presents the crystal-less CMOS frequency reference circuit that is suitable for connectivity applications with a relaxed frequency drift requirement. The presented architecture exploits the open-loop LC oscillator while ensuring constant bias condition, temperature-insensitive operation with an on-chip temperature sensor and digital control logics comprising an adaptive frequency calibration circuit and a non-volatile memory (NVM) performing frequency setup and temperature compensation of the LC oscillator. From 4.12-GHz LC oscillator output frequency, the divide-by-2 circuit followed by the multi modulus divider with 8-256 divide ratio provides 8.05-257.6-MHz output frequencies. The prototype circuit is measured at 27.12-MHz output frequency with ten devices under test and achieves ±50 ppm frequency accuracy (drift) over temperature variation from-40 °C to 80 °C. The measured period jitter in root-mean-squared is 1.32 \text {ps}{\mathrm{ rms}}. Fabricated in the low-cost 0.18 \mu \text {m} CMOS technology, a temperature compensated frequency reference circuit occupies 0.69 mm² and dissipates 15 mA from a 1.8-V supply voltage.