A 9.8-11.5-GHz Quadrature ring oscillator for optical receivers

This paper describes a quadrature ring oscillator that is tunable from 9.8 to 11.5 GHz in a 30-GHz fT BiCMOS technology. The ring oscillator can be used in advanced data clock recovery architectures in optical receivers. The circuit implementation of the oscillator uses transistors as active inductances. Isolation between the oscillator and cascaded circuits, such as buffers and flip-flops, is improved by utilizing the active inductances in a cascode configuration. Carrier to noise ratios better than 94 dBc/Hz at 2-MHz offset are measured with 75-mW dissipation and 2.7-V supply voltage. The evolution in two-stage ring oscillator topologies, leading to the realized design, is discussed in detail on the circuit level