Apparatus and method for generating quadrupled reference clock from single ended crystal oscillator

A method of quadrupling a clock frequency, comprising:

• outputting, via a voltage-controlled oscillator (VCO), a sinusoidal signal according to a first clock frequency;
• generating, via a first buffer, a first digital signal having a 25% duty cycle based on the sinusoidal signal;
• generating, via a second buffer, a second digital signal having a 25% duty cycle based on the sinusoidal signal;
• combining, via a combining module, the first digital signal and the second digital signal to generate a combined digital signal having a 50% duty cycle, the combined digital signal having a second clock frequency that is double the first clock frequency;
• doubling, via a frequency doubling module, the second clock frequency of the combined digital signal to generate an output signal having a third clock frequency that is quadruple the first clock frequency;
• and
• generating a feedback output via a feedback module, wherein the feedback module is coupled to the output signal, and at least one of the generating the first digital signal and the generating the second digital signal is based on the feedback output.

An apparatus for quadrupling a clock frequency, comprising:

• means for outputting a sinusoidal signal according to a first clock frequency;
• means for generating a first digital signal having a 25% duty cycle based on the sinusoidal signal;
• means for generating a second digital signal having a 25% duty cycle based on the sinusoidal signal;
• means for combining the first digital signal and the second digital signal to generate a combined digital signal having a 50% duty cycle, the combined digital signal having a second clock frequency that is double the first clock frequency;
• means for doubling the second clock frequency of the combined digital signal to generate an output signal having a third clock frequency that is quadruple the first clock frequency;
• and
• means for providing feedback coupled to the output signal and generates a feedback output, wherein at least one of the means for generating the first digital signal and the means for generating the second digital signal operates based on the feedback output.