Low-Phase-Noise, High Switching Speed Digitally Controlled Ring Oscillator in 0.18 µm Complementary Metal Oxide Semiconductor

Abstract

In this paper a 14-bit digitally controlled oscillator (DCO) with operating frequency up to 4.2 GHz in 0.18 µm complementary metal oxide semiconductor (CMOS) technology is presented. To improve the phase noise, digital control is used that avoids continuous conduction of transistors and controlling transistors operate either in triode or cutoff region. The circuit uses multiple-loop feed forward architecture to increase the switching speed. The DCO has a wide frequency tuning range from 490 MHz to 4.2 GHz. The measured phase noise of the DCO is -121.2 dBc/Hz at a 4-MHz offset from a 3.86-GHz center frequency and power consumption of 48 mW. Due to the phase noise reduction and high switching speed, the DCO has a -164.1 dBc/Hz figure of merit (FOM) that is an improvement of -4 dBc/Hz over the previously published results in the same technology. The chip area is 300×300 µm2.