On the Design of a High-Performance mm-Wave VCO With Switchable Triple-Coupled Transformer

In this article, we present a circuit technique to design a wide tuning range (TR) voltage-controlled oscillator (VCO). The employed technique extends the TR with a minimal adverse effect on the phase noise (PN). In this context, a switchable triple-coupled transformer, implemented utilizing the topmost three metal layers of the process, is proposed to achieve a wide TR and a low PN. In the proposed configuration, the mutual coupling between the loads is increased while canceling the negative effects of the switches on the transformer performance. Depending on the possible states of the switches used in the secondary and tertiary coils, four overlapping frequency sub-bands are introduced. An extensive set of analysis is provided to support the idea. As a proof-of-concept, a 55-GHz VCO is implemented in a 65-nm CMOS process. Based on the measurement results, the VCO achieves an average PN of -111.9 dBc/Hz at 10-MHz offset over the entire frequency range and a TR of ~18%, from 50.1 to 59.8 GHz, exhibiting a figure of merit incorporating the TR (FOM
_T
) of -184 dBc/Hz at 10 MHz. The VCO core consumes 6.2 mW from a 1-V supply and, excluding the pads, occupies a compact silicon area of 0.06 mm
²
.