Noise-compensated jitter measurement instrument and methods
A test and measurement device includes an input for receiving a test waveform from a Device Under Test (DUT), where the test waveform has a plurality of input level transitions, a selector structured to respectively and individually extract only those portions of the test waveform that match two or more predefined patterns of input level transitions of the test waveform, a noise compensator structured to individually determine and remove, for each of the extracted portions of the waveform, a component of a jitter measurement caused by random noise of the test and measurement device receiving the test waveform, a summer structured to produce a composite distribution of timing measurements with removed noise components from the extracted portions of the test waveform, and a jitter processor structured to determine a first noise-compensated jitter measurement of the DUT from the composite distribution. Methods of determining noise-compensated jitter measurements are also disclosed.
1. A test and measurement device, comprising:
an input for receiving a test waveform from a Device Under Test (DUT), the test waveform having a plurality of input level transitions;
a selector structured to respectively and individually extract only those portions of the test waveform that match two or more predefined patterns of input level transitions of the test waveform;
a noise compensator structured to individually determine and remove, for each of the extracted portions of the waveform, a noise component of a jitter measurement caused by random noise of the test and measurement device receiving the test waveform;
a summer structured to produce a composite distribution of timing measurements with the removed noise components from the extracted portions of the test waveform; and
a jitter processor structured to determine a first noise-compensated jitter measurement of the DUT from the composite distribution.
2. The test and measurement device of claim 1 , in which the summer is structured to exclude tails of the composite distribution to produce a center composite distribution, and in which the jitter processor is further structured to determine a second noise-compensated jitter measurement of the DUT from the center composite distribution.
3. The test and measurement device of claim 2 , in which the first noise-compensated jitter measurement is Jrms and in which the second noise-compensated jitter measurement is JNu.
4. The test and measurement device according to claim 1 , in which a slew rate of transitions that match the first predefined pattern of the test waveform is different than a slew rate of transitions that match the second predefined pattern of the test waveform.
5. The test and measurement device according to claim 1 , in which the noise compensator is structured to fit a histogram of a set of timing data of the extracted portions of the test waveform that match one of the predefined patterns to a curve.
6. The test and measurement device according to claim 5 , in which the noise compensator is structured to fit the histogram of the set of timing data to the curve based on properties of the q-scale.
7. The test and measurement device according to claim 5 , in which the curve is a probability distribution corresponding to a dual-dirac model.
8. A method for determining a jitter measurement of an input signal, the jitter measurement compensated for noise caused by an instrument structured to receive the input signal, the method comprising:
receiving the input signal at the instrument from a Device Under Test (DUT);
producing a test waveform from the received input signal;
selecting two or more portions of the test waveform that respectively match two or more predefined patterns of the input signal;
for each of the two or more selected portions, individually determining a component of jitter caused by instrument noise and individually synthesizing a histogram of timing measurements that compensates for the instrument noise;
summing the noise-compensated histograms of timing measurements of the two or more selected portions to produce a composite probability distribution; and
determining a noise-compensated jitter measurement of the DUT from the composite probability distribution.
9. The method for determining a jitter measurement according to claim 8 , in which individually determining a component of jitter caused by instrument noise includes, for each of the selected two or more portions of the test waveform:
producing a raw histogram of timing errors of the selected portion of the test waveform;
removing a mean value of the timing errors from the raw histogram, and producing a zero-mean histogram; and
performing a dual-dirac analysis to fit the zero-mean histogram to determine Gaussian and Non-Gaussian parts of the zero-mean histogram.
10. The method for determining a jitter measurement according to claim 9 , further comprising for each of the selected two or more portions of the test waveform:
deriving dual-dirac deterministic jitter from the zero-mean histogram; and
deriving random jitter from the zero-mean histogram.
11. The method determining a jitter measurement according to claim 10 , further comprising, for each of the selected two or more portions of the test waveform:
determining a random jitter component added by an effect of a mean slew rate of the selected portion of the test waveform on the random noise of the instrument; and
removing the added random jitter component to produce a compensated random jitter component for the selected portion of the test waveform.
12. The method determining a jitter measurement according to claim 11 , further comprising, for each of the selected two or more portions of the test waveform, synthesizing a compensated dual-dirac model of the selected portion of the test waveform by convolving the compensated random jitter component with the dual-dirac deterministic jitter from the zero-mean histogram.
13. The method determining a jitter measurement according to claim 8 , in which summing the noise-compensated histograms of timing measurements comprises performing a weighted summing of the noise-compensated histograms of timing measurements of the two or more selected portions based at least in part on a relative number of transitions of the input signal in each of the two or more selected portions.
14. The method for determining a jitter measurement according to claim 8 , further comprising:
excluding tails of the combined probability distribution to produce a center summed distribution; and
determining a noise-compensated jitter value from the center summed distribution.
15. A test and measurement device, comprising:
an input for receiving an input signal from a Device Under Test (DUT) and creating a test waveform from the received input signal; and
one or more processors configured to execute code to cause the one or more processors to determine jitter in the input signal that is compensated for noise caused by a device receiving the input signal by:
receiving the input signal at the receiving device;
producing a test waveform from the received input signal;
selecting two or more portions of the test waveform that respectively match two or more predefined patterns of the input signal;
for each of the two or more selected portions, individually determining a component of jitter caused by instrument noise and individually synthesizing a histogram of timing measurements that compensates for the instrument noise;
summing the noise-compensated histograms of timing measurements of the two or more selected portions to produce a composite probability distribution; and
determining a noise-compensated jitter measurement of the DUT from the composite probability distribution.
16. The test and measurement device of claim 15 , in which individually determining a component of jitter caused by instrument noise includes, for each of the selected two or more portions of the test waveform:
producing a raw histogram of timing errors of the first portion of the test waveform;
removing a mean value of the timing errors from the raw histogram, and producing a zero-mean histogram; and
performing a dual-dirac analysis to fit the zero-mean histogram to determine Gaussian and Non-Gaussian parts of the zero-mean histogram.
17. The test and measurement device of claim 16 , in which the one or more processors are further configured to:
derive dual-dirac deterministic jitter from the zero-mean histogram; and
derive random jitter from the zero-mean histogram.
18. The test and measurement device of claim 17 , in which the one or more processors are further configured to, for each of the selected two or more portions of the test waveform:
determine a random jitter component added by an effect of a mean slew rate of the selected portion of the test waveform on the random noise of the receiving device; and
remove the added random jitter component to produce a compensated random jitter component for the selected portion of the test waveform.
19. The test and measurement device of claim 15 , in which the one or more processors are further configured to, for each of the selected two or more portions of the test waveform, synthesize a compensated dual-dirac model of the selected portion of the test waveform by convolving the compensated random jitter component with the dual-dirac deterministic jitter from the zero-mean histogram.
20. The test and measurement device of claim 19 , in which the one or more processors are further configured to sum the noise-compensated histograms of timing measurements by performing a weighted summing of the noise-compensated histograms of timing measurements of the two or more selected portions based at least in part on a relative number of transitions of the input signal in each of the two or more selected portions.
21. The test and measurement device of claim 15 , in which the one or more processors are further configured to:
exclude tails of the combined probability distribution to produce a center summed distribution; and
determine a noise-compensated jitter value from the center summed distribution.