Frequency Tuning Range Extension in LC-VCOs Using Negative-Capacitance Circuits

摘要

We present an experimentally validated capacitance cancellation structure to increase the tuning range (TR) of $LC$ voltage-controlled oscillators (VCOs) with minimal phase noise or power impact. The cancellation is based on an ultrawideband differential active negative-capacitance (NC) circuit. An NC scheme suitable for bottom-biased VCOs is analyzed and combined with a CMOS VCO to cancel the fixed capacitance in the $LC$ tank. The NC structure is further modified to be tunable, enabling additional expansion of the VCO TR. By manipulating the quality factor $(Q)$ of the NC tuning varactor pair, a prototype VCO achieves a maximum TR of 27% in a 130-nm technology, while dissipating 13 mA from a 0.9-V supply. The TR is the highest reported at Q-band, covering from 34.5 GHz to 45.4 GHz. Compared to the reference VCO without an NC circuit, the TR is increased by 38%. The measured worst case phase noise is $-$95 dBc/Hz at 1-MHz offset, and the ${rm FOM}_{T}$ is $-$184.9 dBc/Hz.