A 5.56 GHz Single Core Digitally-Controlled Oscillator With Direct Fine Tuning Steps of 2.85 kHz

As nanotech gets smaller and decreases in size, it is aiding in giving rise to better and more robust smart devices. At the heart of most of these smart devices is some sort of an oscillator. The better the oscillator design and the higher its performance potential, the more robust, more complex, and smarter these devices can become. This work presents a single core DCO (digitally-controlled oscillator) that can step through fine tuning step sizes of as low as 2.85 kHz at frequency of 5.56 GHz without the need of using either dithering, dual -gm pair, inductive switching, expensive FinFET, silicon-on-insulator (SOI), or frequency division (pushing the sub-micron technology of regular 40 nm CMOS to another level). This small resolution is achieved by using fixed MOM caps (highest Q available capacitors in 40 nm TSMC kit). The DCO had 4 banksets on the drain with 16 banks each and 1 bankset on the source with 20 banks. The DCO spanned frequency of 5.41 GHz (all banks closed) to 6.75 GHz (all banks open) with a tuning range of 22.04%. The phase noise (PN) performance of the DCO was 114 dBc/Hz (@ 1MHz offset) at frequency of 6.75 GHz, and had FoM of -181 dBc/Hz @ 1 MHz offset; DCO power consumption was 10 mW.

I. Introduction

As the nanotech gets smaller and reduces in size, it is aiding the fruition of better and more robust smart devices (along with faster communication links) to sprout in the digital domain and electronics atmosphere. Unfortunately with the good also comes a slew of new challenges for designers and engineers; especially as the technology shifts from an analog paradigm to a digital one due to confinements and restrictions of the physically quantized fabrication limits (such as transistor gate width restraints). At the heart of most of these smart devices is some sort of ticking clock with a tracker: such as a phase-locked loop (PLL), delay locked loop (DLL), or an injection locked synchronizer; and the actual timing ticker is generated by some sort of oscillator (whether ring, LC or otherwise). LC tanked oscillators (especially the negative gm (-gm) pair variety) tend to be excellent for low phase noise (PN) generation. And as the trend moves towards a digital world, so too is this type of oscillator.