Low Noise Phase CMOS Quadrature VCO with Superharmonic Coupling Using Cross-Couple Pair

Seyed Reza Hadianamrei,Masoud Sabaghi,Maziyar Niyakan Lahiji,Mehdi Rahnama

doi:10.4236/cs.2011.24039

Abstract

This paper aims to introduce a quadrature VCO (voltage control oscillator) which applies superharmonic coupling. The presented quadrature VCO is suitable to be used, both with 2 × subharmonic mixers, as well as 4×subharmonic mixers. It would be impossible to avoid the presence of harmonics in CMOS VCO circuits. These harmonics are in general, undesirable signals which tend to accompany the desired fundamental signal. There are common-mode nodes (similar to those in the two source nodes in a cross-coupled VCO) in deferential VCO at which higher-order harmonics are present while the fundamental is absent in essence. We can make use of these second-order harmonics which are present at the common-mode nodes of two VCO in order to implement a quadrature connection between the fundamental outputs. The technique through which this is done is called superharmonic coupling. This CMOS quadrature VCO which applies active superharmonic coupling puts an excellent performance in show, with an output power –0.942 dBm for fundamental and –9.751 dBm for subharmonic, phase noise –107.2 dBc/Hz for fundamental and –114.8 dBc/Hz at a 1MHz offset. All of circuit applied are designed and simulated by ADS, 2008.

Highlights

Oscillators are fundamental components in wireless communications systems that can be used for several applications
This paper aims to introduce a quadrature VCO which applies superharmonic coupling
The technique through which this is done is called superharmonic coupling. This CMOS quadrature VCO which applies active superharmonic coupling puts an excellent performance in show, with an output power –0.942 dBm for fundamental and –9.751 dBm for subharmonic, phase noise –107.2 dBc/Hz for fundamental and –114.8 dBc/Hz at a 1MHz offset

Summary

Introduction

Oscillators are fundamental components in wireless communications systems that can be used for several applications. Communication systems that use phase shift keying modulation frequently require a pair of LO signals that are in quadrature, or 90 ̊ out-of-phase. Quadrature VCO (voltage control oscillator) is one of the most important components in direct conversion transceivers. These VCOs are of a basic role in image-rejection techniques which are based on the appropriate phasing of the signals. They eliminate the immense and non-planar high-frequency filters. It should be added that, some digital radio communication systems (e.g. GSM and DECT) in which complex digital modulation schemes are applied in order to reduce the signal bandwidth to the possible minimum level, need quadrature VCO [1]. If the real values of R and C are not accurate, it may result in errors in the quadrature which, in turn, necessitate compensation of some form [2]

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Conclusion