Method and Apparatus for Analyzing Phase Noise in a Signal from an Electronic Device

Abstract

An apparatus and method for analyzing phase noise in a signal. A plurality of signal samples, each signal sample representing a value of phase noise in a signal-under-test at a corresponding offset frequency, and filter data representing filter characteristics on a first side of a spectrum boundary, are used to derive filtered signal samples. A measure of noise is derived from the filtered signal samples. This abstract is not to be considered limiting, since other embodiments may deviate from the features described in this abstract.

What is claimed is: 
     
         1 . A method comprising:
 a) using a noise-measurement system to derive a plurality of signal samples, each signal sample representing a value of phase noise in a signal-under-test (SUT) at a corresponding offset frequency;   b) creating derived signal samples on a first side of a spectrum boundary from the plurality of signal samples, wherein the creating comprises representing phase noise located on a second side of the spectrum boundary that folds across the spectrum boundary onto the first side of the spectrum boundary; and   c) filtering on the first side of the spectrum boundary the derived signal samples.   
     
     
         2 . The method of  claim 1 , further comprising:
 d) deriving a measure of noise from the filtered derived signal samples.   
     
     
         3 . The method of  claim 2 , wherein the SUT represents a clock timing signal having an SUT clock frequency, and the spectrum boundary is located at an offset frequency equal to half the SUT clock frequency. 
     
     
         4 . The method of  claim 3 , wherein the noise-measurement system comprises a phase noise analyzer. 
     
     
         5 . The method of  claim 3 , wherein the noise-measurement system comprises a spectrum analyzer. 
     
     
         6 . A method comprising:
 a) using a noise-measurement system to derive a plurality of signal samples on a first side of a spectrum boundary from a signal-under-test (SUT), each signal sample representing a value of phase noise in the SUT at a corresponding offset frequency;   b) deriving estimated higher-frequency signal samples from at least one of the signal samples in the plurality of signal samples, where the estimated higher-frequency signal samples represent phase noise on a second side of the spectrum boundary;   c) filtering a set of signal samples created from the plurality of signal samples and the estimated higher-frequency signal samples; and   d) deriving a measure of noise from the filtered signal samples.   
     
     
         7 . The method of  claim 6 , wherein the SUT represents a clock timing signal having an SUT clock frequency, and the spectrum boundary is located at an offset frequency equal to half the SUT clock frequency. 
     
     
         8 . The method of  claim 7 , wherein the noise-measurement system comprises a phase noise analyzer. 
     
     
         9 . The method of  claim 7 , wherein the noise-measurement system comprises a spectrum analyzer. 
     
     
         10 . A method, comprising:
 a) using a measurement system to derive a plurality of signal samples, each signal sample representing a value of phase noise in a signal-under-test (SUT) at a corresponding frequency;   b) creating derived signal samples from the plurality of signal samples, wherein the derived signal samples account for aliased phase noise; and   c) filtering the derived signal samples.   
     
     
         11 . The method of  claim 10 , further comprising:
 d) making a product resulting from the filtered derived signal samples.   
     
     
         12 . The method of  claim 11 , wherein the making of the product uses the filtered derived signal samples to validate a level of performance for which the product is specified, failing which the product is not made. 
     
     
         13 . The method of  claim 12 , wherein the validation uses test limits derived from the filtered derived signal samples to determine whether the product passes or fails the level of performance. 
     
     
         14 . The method of  claim 13 , wherein passing the test limits guarantees by design the level of performance for the product. 
     
     
         15 . The method of  claim 12 , wherein the SUT represents a clock timing signal. 
     
     
         16 . The method of  claim 13 , wherein the measurement system comprises one of:
 a phase noise analyzer and a spectrum analyzer.