Patent ID: 7015766
Filing Date: 2006-03-21
Classification: H03K,H03L

Abstract:
1. A voltage-controlled oscillator (VCO) comprising: an output clock having an output frequency; an input having an input voltage that is varied to vary output frequency; a variable current source, responsive to the input, for varying a current to a source node in response to the input voltage; a ring oscillator that generates the output clock, the ring oscillator having the source node supplying current to transistors in the ring oscillator wherein varying a source voltage of the source node varies the output frequency of the output clock generated by the ring oscillator; a bypass capacitor coupled to the source node; and an active resistor coupled in parallel with the ring oscillator to the source node, the active resistor having a series resistor and a series transistor in series, whereby the active resistor in parallel with the ring oscillator lowers an R-C time constant of the source node.