A voltage controlled current source provides controlled current to a
current controlled oscillator in a high frequency phase-locked loop clock
generator. The voltage controlled current source receives a first control
signal and a set of second control signals indicative of a phase
difference between the output signal of the clock signal generator and a
reference frequency. It uses those control signals to adjust the
current-controlled oscillator. A level shifter coupled to the
current-controlled oscillator amplifies the oscillator signals to full
rail and adjusts the duty cycle at its output to 50% to produce the clock
signal generator output signal.