Modulation noise estimation mechanism

An apparatus for testing an oscillator in a phase locked loop having a phase locked loop, comprising:

• means for averaging phase error samples produced by said phase locked loop;
• means for subtracting said average from a current phase error sample to yield a normalized phase error, wherein said normalized phase error corresponds to the phase modulation noise of said oscillator;
• means for generating an exception event if said normalized phase error exceeds a threshold;
• and
• means for repeating said functions of averaging, subtracting and generating over a period of time and outputting a test failure indication if the number of exception events exceeds a maximum criterion and a test pass indication otherwise.

An apparatus for testing an oscillator in a phase locked loop, comprising:

• first means for measuring a phase error signal within said phase locked loop, wherein said phase error signal corresponds to the phase noise of said oscillator;
• second means for comparing a plurality of phase error signal samples over a period of time to a threshold and generating an exception event each time a phase error signal sample exceeds said threshold;
• and
• generating a test failure indication if the number of exception events exceeds a defined limit and generating a test pass indication otherwise.

A method of testing an oscillator in a phase locked loop, said method comprising the steps of:

• generating a normalized phase error signal from a plurality of phase error samples generated by said phase locked loop;
• and
• counting the number of times said normalized phase error signal crosses a threshold within a predefined period of time, wherein the count represents an estimate of the phase modulation noise of said oscillator;
• and
• failing said oscillator if said count exceeds a predefined maximum, and passing said oscillator otherwise.