Non-trimmable LC oscillator for all CMOS frequency control

Abstract

A fully integrated all CMOS oscillator frequency reference is presented that is suitable for crystal replacement in relaxed requirement applications. The frequency reference constitutes a new approach of CMOS frequency control based on a reference-less non-trimmable LC oscillator (LCO) with a resonance frequency of approximately 3.15 GHz and a low jitter fractional divider. The fractional frequency divider consists of an integer divider and a programmable delay and thus provides a wide range of possible output frequencies from 1 to 180 MHz. A complex control logic comprising a nonvolatile memory (NVM) performs the calibration, frequency setup, and temperature compensation of the device. A planar magnetic decoupling structure is used to reduce the sensitivity of the LCO to its environment. This implementation allows the assembly of the LCO chip in a standard plastic package without using a Faraday shield. The device achieves an initial frequency stability of ±50 ppm over a temperature region of -20 to 85°C. The presented architecture overall dissipates 6.5mA from a 1.8-3.6V power supply (buffer neglected) and is competitive to already existing integer divider based LCO frequency reference realisations.