Design of Wide Tuning-Range CMOS VCOs Using Switched Coupled-Inductors

Abstract

Two designs of voltage-controlled oscillators (VCOs) with mutually coupled and switched inductors are presented in this paper to demonstrate that the tuning range of an LC VCO can be improved with only a small increase in phase noise and die area in a standard digital CMOS process. Particular attention is given to the layout of the inductors to maintain across the tuning range. In addition, different capacitive coarse-tuning methods are compared based on simulated and measured data obtained from test structures. Implemented in a 90 nm digital CMOS process, a VCO with two extra coupled inductors achieves a 61.9% tuning range with an 11.75 GHz center frequency while dissipating 7.7 mW from a 1.2 V supply. This VCO has a measured phase noise of 106 dBc/Hz at 1 MHz offset from the center frequency resulting in a higher figure-of-merit than other recently published VCOs with similar operating frequencies. In addition, the area overhead is only 30% compared to a conventional LC VCO with a single inductor.Index Terms-Integrated transformers, phase noise, radio-frequency (RF) CMOS, switched coupled inductor, tuning range, voltage-controlled oscillator (VCO).

A Survey on FM-UWB Transceivers

“…Hence, LC VCO is a better choice for FM-UWB applications. Furthermore, several LC VCOs operating at the UWB frequencies have been reported [23][24][25][26][27][28][29][30][31] and are widely used in FM-UWB transmitters for RF carrier generation [12][13][14][15], [32][33][34]. Table 1 provides a comparison among the most recent published VCOs operating at the UWB frequencies.…”

A 5–5.47GHz LC-VCO using varactor configuration in 0.18um CMOS technology

“…This is around 61.9% at the centre frequency of 11.75 GHz. Due to usage of MOS switches additional noise is introduced overcoming the advantage of mutually coupled switched inductor [4].…”

A 5.12–12.95GHz triple-resonance low phase noise CMOS VCO for software-defined radio applications

“…However, this technique requires large silicon area and therefore increases the cost. Other techniques have been reported to widen the oscillator tuning range including VCOs exploiting switched inductors [2] and coupled inductors [3]- [6]. The VCOs based on switched inductors suffer from poor phase noise performance due to the loss of the switches inside the tank.…”