CMOS second-harmonic quadrature voltage controlled oscillator using substrate for coupling

In this work, a new circuit configuration for second-harmonic quadrature voltage controlled oscillator (QVCO) with CMOS technology is proposed. The proposed QVCO is made by coupling two identical cross-connected VCOs. The coupling elements (two resistors and two capacitors) do not increase the power consumption of the core VCOs and do not disturb the resonant frequency of the tank circuit in the core VCOs and also, according to the simulations the coupling elements do not adversely affect the phase noise. The role of the substrate terminal of cross-connected MOSFETs of the core oscillators as common mode nodes is demonstrated. Using this node for coupling makes it possible to eliminate the tail transistors in the core oscillators and therefore the circuit can operate with supply voltages as low as 0.5 V. Using the same method to couple more than two core oscillators, results in a multiphase VCO.