Patent ID: 7321269

Claim:
A voltage controlled ring oscillator comprising: a number N primary inverting stages each having an input and an output, wherein the N primary inverting stages are coupled in series with the output of the Nth primary inverting stage coupled back to the input of the first primary inverting stage; and N modulating inverting stages each having a first input, a second input and an output, wherein the first input of modulating inverting stage numbered M is coupled to an input of a primary inverting stage numbered M from the N primary inverting stages, the output of modulating inverting stage numbered M is coupled to an output of the primary inverting stage numbered M from the N primary inverting stages, the second input of modulating inverting stage numbered M is coupled to an output of a primary inverting stage numbered (M+2)(modulo N) from the N primary inverting stages, and a signal level on the output of each of the N modulating inverting stages is varied in response to a voltage level of a common control voltage and corresponding voltage levels on the first and second inputs of each of the N modulating inverting stages, and wherein the modulating inverting stages each comprises: a first inverter having an input coupled to the first input of the modulating inverting stage and an output; a first pass gate having an input coupled to the output of the first inverter, a pass gate output coupled to the output of the modulating inverting stage, and a first control input coupled to the common control voltage; a second inverter having an input coupled to the second input of the modulating inverting stage and an output; a second pass gate having an input coupled to the output of the second inverter, a pass gate output coupled to the output of the modulating inverting stage, and a second control input coupled to the common control voltage; and a third inverter having an input coupled to the second input of the modulating inverting stage and output coupled to the output of the second inverter.