A wideband low-phase-noise CMOS VCO

Abstract

A CMOS VCO has been designed and fabricated in a commercial 0.25µm CMOS process. Using a combination of switched binary-weighted capacitors and standard varactors, this VCO achieves a 28% tuning range with a control voltage ranging from 0-2 V, while maintaining a tuning sensitivity of less than 75 MHz/V over its entire frequency range. Compact choke inductors are used in place of resistors to provide a low noise bias point to the varactors. The choke inductors achieve more than 90 nH of effective inductance while consuming a die area of only 92 x 92 µm 2 . The measured single-sided phase noise is -127 dBc/Hz at a 600 kHz offset from a 1.24 GHz carrier when the VCO core is drawing 3.6 mA from a 2 V supply. IntroductionVoltage controlled oscillators (VCOs) are essential building blocks of modern communication systems. The VCO performance in terms of phase noise, tuning range, and power dissipation determines many of the basic performance characteristics of a transceiver. The current trend to utilize multi-band multi-standard receivers and also very wideband systems is driving the effort to create new VCO topologies with wide tuning range, low phase noise, and low power consumption. Whereas relaxation oscillators easily achieve very wide tuning range (i.e. 100% or more), their poor phase noise performance disqualifies them in most of today's wireless and wireline applications. Because LC VCOs have been successful in narrowband wireless transceivers, there is a growing interest to extend their tuning range. Recently, several wideband CMOS LC VCOs have been demonstrated using a variety of techniques [1][2][3][4]. The high intrinsic C max /C min of inversion-or accumulation-type MOS varactors supports a very wide tuning range and their Q is sufficiently high that good phase noise performance can be maintained. However in practice, the overall phase noise performance is also highly dependent on the tuning sensitivity of the VCO, since noise from preceding stages of the frequency synthesizer is inevitably injected onto the VCO control input. Hence, aside from achieving a high raw tuning range, practical wideband VCO solutions must properly limit the overall VCO tuning sensitivity.

Design of VCO with a Differential Tunable Active Inductor

“…By increasing g ds5 and g ds6 , the inductance of active inductor is decreased, as presented in (2). Also the size of M 1 -M 2 transistors has an effect on the amount of active inductor conductance.…”

“…Practically the tuning rang of VCO is low and these makes them unsuitable for wideband applications. By utilizing switched capacitors [1], [2] and switched inductors [3], [4], tuning rang of wide frequency can be obtained. The disadvantages are: enlarging the chip area and complexity of control mechanism.…”

Design of reconfigurable RF front-end for multi-standard receiver using switchable passive networks

“…Tuning of the resonant center frequency can be done in a few ways, i.e., by using the varactor, tunable active inductor [12], and switched capacitor array [13,14] or switched inductor array [15]. But all conventional tuning methods have limitations.…”

A Voltage Controlled Oscillator for a Phase-Locked Loop Frequency Synthesizer in a Silicon-on-Sapphire Process

“…They also help in reducing the finite varactor loss by a factor of (C coupling +C varactor ) 2 /C coupling 2 and decrease phase noise [15]. Additional source-follower amplifiers were also added to the core to provide more isolation to the entire VCO circuit A major issue with the first VCO design was its inability to handle phase variation in a 3:1 VSWR load mismatch.…”