Distortion measurement for limiting jitter in PAM transmitters

Patent metadata

Field	Value
Publication number	US-8982938-B2
Application number	US-201213713309-A
Country	US
Kind code	B2
Filing date	Dec 13, 2012
Priority date	Dec 13, 2012
Publication date	Mar 17, 2015
Grant date	Mar 17, 2015

Abstract

Methods and test equipment for measuring jitter in a Pulse Amplitude Modulated (PAM) transmitter. Under one procedure, a first two-level PAM signal test pattern is used to measure clock-related jitter separated into random and deterministic components, while a second two-level PAM signal test pattern is used to measure oven-odd jitter (EOJ). Under another procedure, A four-level PAM signal test pattern is used to measure jitter-induced noise using distortion analysis. Test equipment are also disclosed for implementing various aspects of the test methods.

First claim

What is claimed is:

1. A method for measuring jitter in a four-level Pulse Amplitude Modulated (PAM4) transmitter, comprising:
employing a first two-level PAM4 signal test pattern to measure clock-related jitter separated into random and deterministic components;
employing a second two-level PAM4 signal test pattern to measure oven-odd jitter (EOJ); and
employing a four-level PAM4 signal test pattern to measure jitter-induced noise using distortion analysis.

2. The method of claim 1 , wherein the four-level PAM4 signal test pattern comprising a PAM4 signal having a first level comprising a lowest voltage level, a fourth level comprising a highest voltage level, and second and third levels comprising intermediate voltage levels between the lowest and highest voltage level, and wherein each of the first two-level PAM4 signals employ the first and fourth PAM4 signal levels.

3. The method of claim 1 , wherein the first two-level PAM4signal test pattern comprises a ‘03’ pattern that is periodical at 2 unit intervals (UI), wherein the 0 and 3 respectively correspond to a lowest and highest signal level of a PAM4 signal.

4. The method of claim 1 , wherein the second two-level PAM4 signal test pattern comprises an odd number of repetitions of ‘03’ followed by an even number of repetitions of ‘30’, wherein the 0 and 3 respectively correspond to a lowest and highest signal level of a PAM4 signal.

5. The method of claim 4 , wherein the second two-level PAM4 signal test pattern comprises 15 repetitions of ‘03’ followed by 16 repetitions of ‘30’, and the test pattern is periodical at 62 unit intervals (UI).

6. The method of claim 1 , wherein measuring the clock-related jitter components comprises:
capturing a signal waveform from a transmitted two-level PAM4 signal test pattern;
calculating zero-crossing times for the captured signal;
calculating an average pulse width derived as a function of the zero-crossing times; and
calculating a phase jitter series.

7. The method of claim 6 , further comprising:
applying a 1 st -order discrete high-pass filter to the phase jitter series to produce a set of results;
sorting the set of results in increasing order;
estimating first and second cumulative distribution function (CDF) values from the set of results; and
calculating clock random jitter (CRJ) and deterministic clock deterministic jitter (CDJ) as a function of the first and second CDF values.

8. The method of claim 7 , wherein the first and second CDF values are respectively denoted as J 5 and J 6 , and wherein a root mean square (RMS) value for random jitter (CRJ RMS ) and CDJ are calculated according to:

[

CRJ
RMS

CDJ

]

=

[

2
⁢

Q

-
1

⁡

(

0.5
×

10

-
6

)

1

2
⁢

Q

-
1

⁡

(

0.5
×

10

-
5

)

1

]

-
1

⁡

[

J
6

J
5

]

where Q −1 is the inverse Q-function.

9. The method of claim 1 , wherein measuring EOJ comprises:
capturing a signal waveform from a transmitted two-level PAM4 signal test pattern comprising an even portion and an odd portion;
calculating an average zero-crossing time for each of a plurality of transitions relative to a start of the test pattern;
calculating the widths of a plurality of even pulses corresponding to even portions of the captured signal waveform;
calculating the widths of a plurality of odd pulses corresponding to odd portions of the captured signal waveform; and
calculating EOJ as a function of the widths of the even pulses and the odd pulses.

10. The method of claim 9 , wherein the EOJ is calculated as half of the magnitude between the difference between the mean width of the even pulses and the mean width of the odd pulses.

11. The method of claim 9 , wherein the widths of the even pulses and odd pulses exclude part of the even and odd portions of the test pattern.

12. A method for measuring distortion in a transmitted signal, comprising:
transmitting a four-level Pulse Amplitude Modulated (PAM4) test pattern for each of a plurality of lanes;
capturing N unit interval (UI) of the test pattern, where N is an integer multiple of the test pattern's length in UI, with M samples per UI to ob

Assignees

• Ran Adee O
• Intel Corp

Inventors

• Ran Adee O

Classifications

• H04L1/248 Primary

  Distortion measuring systems (measurement of non-linear distortion G01R23/20; measuring characteristics of individual pulses, e.g. deviation from pulse flatness, rise time, duration G01R29/02) · CPC title

• G01R29/027

  Indicating that a pulse characteristic is either above or below a predetermined value or within or beyond a predetermined range of values · CPC title

• G01R31/31709 Primary

  Jitter measurements; Jitter generators (measuring jitter, noise figure or signal-to-noise ratio per se G01R29/26; analysis of tester signals G01R31/31901) · CPC title

• H04L1/24 Primary

  Testing correct operation · CPC title

• H04L1/205 Primary

  jitter monitoring · CPC title