An X-band LC VCO Using a New Boosted Active Capacitor With 53 % Tuning Range and -202.4 dBc/Hz FoMT

This paper presents a new boosted active-capacitor topology for wide tuning range voltage-controlled oscillators (VCO). A tuned inductor-based active-impedance-conversion circuit (LAIC) is used to multiply the capacitance of a capacitor bank and the negative-transconductance of LAIC in the proposed region of operation but without increasing losses. A boosted active-capacitor prototype in 65 nm CMOS process achieves a capacitance tuning ratio of 7.8 and a quality factor of higher than 20 across VCO's tuning range. An X-band VCO prototype with the proposed boosted active-capacitor achieves a 53 % measured fractional frequency tuning range and phase noise of -115 dBc/Hz at 1 MHz offset, resulting in an excellent figure-of-merit-with-tuning-range (FoMT) of -202.4 dBc/Hz.

I. Introduction

To support the increasingly higher data rate demands, carrier frequency for wireless communications are moving towards largely unoccupied mm-Wave bands with wide bandwidth, such as 28 GHz for 5G, 60 GHz for WiFi, and 70 GHz for microwave backhaul links, and so on. These wireless communication systems require a high-performance wide tuning-range (TR) LC VCO to generate the desired carrier frequencies either directly, or by using sub-harmonic injection-locked oscillators [1]–[2] in which the main highperformance VCO oscillates at a lower frequency because the phase-noise versus tuning range trade-offs are comparatively relaxed at lower oscillation frequencies.