A 19.5-GHz 28-nm Class-C CMOS VCO, With a Reasonably Rigorous Result on 1/f Noise Upconversion Caused by Short-Channel Effects

Class-C operation is leveraged to implement a K-band CMOS voltage-controlled oscillator (VCO) where the upconversion of 1/f current noise from the cross-coupled transistors in the oscillator core is robustly contained at a very low level. Implemented in a bulk 28-nm CMOS technology, the 12%-tuning-range VCO shows a phase noise as low as -112 dBc/Hz at 1-MHz offset (-86 dBc/Hz at 100 kHz offset) from a 19.5 GHz carrier while consuming 20.7 mW, achieving a figure of merit (FoM) of -185 dBc/Hz. The design is complemented by a theoretical investigation of 1/f noise upconversion caused by short-channel effects in the cross-coupled transistors, obtaining the first instance of a closed-form phase noise expression in the 1/f³ region.

I. Introduction

Frequency synthesizers with ever lower phase noise are fundamental components in most innovative integrated systems, spanning from wireless and wireline communications to anti-collision systems, radar imaging devices, optical networks, and so on. In particular, the phase noise of the voltage-controlled oscillator (VCO) can be the ultimate bottleneck for the low phase noise performance required by the systems, such as the fifth-generation cellular network technology (5G). In 5G systems, the goal of providing an ultra-high user data rate requires operation at millimeter waves (mm-waves) and a signal modulation using large symbol constellations—hence, a very low phase noise frequency generation at mm-waves is crucial. To achieve this goal, it is often more convenient to operate the VCO at lower frequencies, recovering the desired carrier frequency using frequency multiplication [1]. The design of a harmonic VCO in the -band is, therefore, very attractive, taking advantage of a higher attainable quality factor for the LC tank at those frequencies, which results in a lower phase noise and power consumption, while the lower frequency of operation is also favorable for a wider tuning range.