A Colpitts CMOS quadrature VCO using direct connection of substrates for coupling

Authors:
Emad Ebrahimi;Sasan Naseh
Affiliations:
Electrical Engineering Group of Engineering Department, Ferdowsi University of Mashhad, Mashhad, Iran;Electrical Engineering Group of Engineering Department, Ferdowsi University of Mashhad, Mashhad, Iran
Venue:
IEEE Transactions on Very Large Scale Integration (VLSI) Systems
Year:
2013

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Abstract

A new low-phase noise low-power quadrature voltage-controlled oscillator (QVCO) using differential Colpitts oscillator is presented. The proposed QVCO is composed of two identical current-switching differential Colpitts VCOs in which the first core VCO is coupled to the second in an in-phase manner, and the second core VCO is coupled to the first in an anti-phase manner. To couple the two core VCOs, the substrates of the cross-connected transistors as well as the substrates of MOS varactors are used; alleviating the need for any extra elements for coupling, which could add noise and increase power dissipation. A linear (sinusoidal) analysis is presented that confirms that the proposed circuit generates quadrature waveforms. The proposed coupling technique can be generalized to N differential Colpitts VCOs for multiphase signals generation.