A Crystal-Less Programmable Clock Generator with RC-LC Hybrid Oscillator for GHz Applications in 14 nm FinFET CMOS

Abstract

This paper presents a crystal-less programmable clock generator. The programmable clock generator takes advantages of both RC and LC oscillators. The frequency reference is generated by the RC oscillator without using expensive external crystals. The sawtooth signal generated from the RC oscillator is sampled by low phase-noise differential clocks which are divided from the LC oscillator. The timing information is then amplified by the sampler which uses hysteresis. An additional block, gain adjuster (GA), reduces lock time and dithering. After the system gets locked, it achieves 0.01 %/V and 25.5 ppm/°C frequency variations for 100 MHz generated clock. The 14 nm FinFET CMOS programmable clock generator draws 28 mA current from a single 1.8 V supply and occupies an active area of 0.12 mm2, It achieves 163 dBc/Hz FoM for 100 MHz test clock.