N-stage ring connected voltage controlled oscillator

Abstract

A VCO includes an oscillator and a controller for controlling the operation of the oscillator. The oscillator is formed by connecting odd number of stages of delay circuits in a ring form. The controller creates a second control voltage based on an input first control voltage. The second control voltage is set in a symmetrical relation to the first control voltage with respect to an intermediate potential between the power supply and the ground set as a reference. Each of the delay circuits includes an inverter, first and second current control circuits, and first and second current value setting circuits. The inverter includes a first transistor of first conductivity type and a second transistor of second conductivity type to receive and output a signal. The first current control circuit is connected between the first transistor and the ground, for controlling a current flowing in the first transistor when the first transistor is set in the conductive state according to the first control voltage. The first current value setting circuit sets the minimum value of the current flowing in the first transistor. The second current control circuit is connected between the second transistor and the power supply, for controlling a current flowing in the second transistor when the second transistor is set in the conductive state according to the second control voltage. The second current value setting circuit sets the minimum value of the current flowing in the second transistor.