A fully differential VCO cell with active inductor load for GBPS serial links

This paper investigates the characteristics of cross-coupled fully differential VCO cell with resistive, current source, and active inductor loads. We show that the cross-coupled VCO cell with resistive load exhibits smaller rise time as compared that with current-source load. The rise and fall times of the VCO cell with self-biased active inductor load are significantly smaller as compared with those with resistive and current-source loads. The power of the equivalent noise source of the active inductors and that of the VCO cell with the active inductor at state transitions are derived. Using the results from Kim et al., (1994), we show that the proper choose of the resistor value of the self-biased active inductor can achieve a minimum timing jitter of the VCO.