Realization of a low-voltage and low-power Colpitts quadrature oscillator

An oscillator for generating a differential quadrature signal dedicated for RF applications is proposed. The topology is based on a direct coupling between two identical differential Colpitts oscillators, requiring no additional coupling stages and hence reducing the current consumption. A theory on the lowering of the oscillating frequency of the quadrature configuration compared to the single-ended configuration has been established and is in good agreement with the experimental results using discrete components operating in a range of kHz and few MHz regions. The simulated figure-of-merit of the proposed Colpitts quadrature oscillator operating in GHz range favorably compares with a single-stage differential Colpitts oscillator and a conventional negative-resistance quadrature oscillator using identical inductor and varactor models