A 19 GHz Circular-Geometry Quad-Core Tail-Filtering Class-F VCO with -115 dBc/Hz Phase Noise at 1 MHz Offset in 65-nm CMOS

This paper presents a CMOS circular-geometry quad-core voltage-controlled oscillator (VCO) with class-F operation and tail filtering to achieve ultra low phase noise in K band. The use of class-F operation in a circular-geometry multicore VCO further lowers phase noise but results in new mode ambiguity. We introduce cross-coupled narrow and thin metal traces in the class-F transformer secondary loop to suppress this new mode ambiguity. Also, we extend the circular geometry design to the VCO tail LC filters, reducing the chip area. A proof-of-concept prototype is fabricated in a standard 65 nm CMOS technology. In measurement, the VCO operates from 17.9 to 20.7 GHz. At 19 GHz, the VCO achieves a phase noise of -115 dBc/Hz at 1 MHz offset with a figure of merit (FoM) of -188.4 dBc/Hz.