A Temperature Compensated RF $LC$ Clock Generator With ±50-ppm Frequency Accuracy From −40 °C to 80 °C

Abstract

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.