Tektronix WFM2300 Guide de l'administrateur

How-to-Guide

SDI Eye and Jitter Measurements

WFM2300 Portable Waveform Monitor

SDI Eye and Jitter Measurements How-to Guide

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Table of Contents

Introduction ………………………………………………………………………… 3

Troubleshooting the SDI Signal Path …………………………….……………. 3

How to Configure Video Session Display ……………………….……………. 4

How to Configure SDI Status Display ……………………….………………… 5

Cable Stress Loop ……………………………………………….……………….. 7

How to Configure SDI Stress Loop Amplitude …………….………………… 9

How to Configure Eye Measurements ……………………….………………… 10

Enabling Pseudo Color Display …………………………….…………………... 12

Measuring Jitter within an SDI Signal …………………….…………………… 14

Enabling Infinite Persistence Mode …………………….……………………… 18

Conclusion ………………………………………………….……………………… 20

SDI Eye and Jitter Measurements How-to Guide

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Serial Digital Interface (SDI) Physical Layer Monitoring

Reliable transmission of the SDI signal from point A to point B is dependent on a variety of factors such as:

Amplitude of the Signal

Overshoot

Undershoot

Jitter

Rise and Fall Time of the Transitions

These parameters are affected by the cable length, that over longer runs of cable will introduce amplitude

and frequency losses to the signal resulting in longer rise and fall times of the signal. Overshoot and

undershoot are typically a result of incorrectly terminated devices or panels which introduce reflections into

the signal. Additionally deformation of the cable can also introduce reflections into the signal along with cable

loss. Active devices may introduce jitter into the signal as the signal is processed or genlocked to a

reference signal. The first stage of troubleshooting a physical layer issue is to verify the link by using CRC

(Cyclic Redundancy Code) words to verify the link is error free. The Video Session display will shows

statistics of the CRC Errors.

Troubleshooting the SDI Signal Path

Error Free signal path, check for CRC (HD or 3G) or EDH (Error Detection Handling) if present

within SD-SDI signals. Use the video session of the WFM2300 to determine this.

Determine if the signal path has a safety margin by adding an additional length of cable or using

a stressing signal. Does the addition of the cable length or stress cause CRC issues or loss of

the signal? The cable simulator of the WFM2300 adds 20m of Belden 1694A cable along with

the ability to add an interfering signal or use the internal test signal generator with the

pathological test signal to stress the signal path.

Estimate the cable length of the signal path to determine if the receiving device is operating

within its specification, using the SDI Status displays of the WFM2300.

Check at various points along the transmission path to characterize the SDI signal.

Use the Eye displays of the WFM2300 to characterize the health and possible artifacts present

within the SDI signal along the signal path.

Use the Jitter thermometer within the eye, jitter and SDI status display of the WFM2300 to

determine the timing and alignment jitter present within the signal.

Use the Jitter display in two-field sweep to characterize the jitter within the signal and use the

high pass filters to determine the amount of jitter present within each frequency band.

SDI Eye and Jitter Measurements How-to Guide

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How to Configure Video Session Display

1. Select one of the tiles (1, 2, 3 or 4) using the Display Select and press the STATUS button.

2. Push and Hold the STATUS button to display the Status menu.

3. Using the general knob or up/down arrow keys navigate to and select Display Type as shown in

Figure 1.

4. Press SEL to enter the submenu and navigate to Video Session to show a summary of video

parameters of the current video signal as shown in Figure 1.

Figure 1. Video Session Display.

For HD-SDI, Dual Link and 3G-SDI signals there is a CRC calculated every line with a value produce

one for Y Luma and one for C Chroma samples. This is shown in the lower statistics information of

Figure 1.

If the signal attached to the WFM2300 is error free then the Status will show OK in green.

If a CRC error occurs then this will show in the Video Session display in red and a count of the

number of values that have occurred during the session will be displayed.

In order to determine the error rate of CRC errored seconds, the user may need to monitor the signal

path for several minutes or hours. Within the Status menu for the Video Session display the user can

reset the duration of the session and the statistics will be reset too.

See Figure 1. Video Session menu All Sessions Reset)

NOTE:

For standard definition (SD-SDI) signals there is no embedded CRC check and instead an Error

Detection Handling ancillary packet must be inserted by the device in order to provide CRC check of

the signal.

SDI Eye and Jitter Measurements How-to Guide

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If you see errors every minute or every second then this is an indication that the signal is getting close to the

digital cliff and there is a problem in recovering the clock and data of the signal within the receiver. Not all

receivers are identical and this can affect the devices ability to recover the clock and data.

The WFM2300 has been designed with a robust equalizer and receiver to allow the user to determine signal

issues. Some devices may fail before the WFM2300 and so it is important to check the manufacture’s

specification for cable length distance and type of cable. The SDI status display provides an estimated cable

length measurement based on selection of specific cable types.

NOTE:

Most manufacturers specify the performance of their equipment to a specific cable type typically Belden

8281 or Belden 1694A and it is recommend to select this cable type when estimating the cable length of

the device, even though the cable being used may not be this type of cable.

How to Configure SDI Status Display

1. Select one of the tiles (1, 2, 3 or 4) and press the STATUS button.

2. Push and Hold the STATUS button to enable the menu.

3. Using the up and down arrows to navigate to Display Type and press right arrow to select the

sub menu as shown in Figure 2.

4. Select SDI Status display to show a summary of physical layer parameters of the current video

signal as shown in Figure 3.

Figure 2. SDI Status Display Type menu.

SDI Eye and Jitter Measurements How-to Guide

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Figure 3. SDI Status Display showing physical layer measurement summary.

The SDI Status provides a summary of the physical layer measurements of the SDI input. Jitter and Cable

Loss Thermometer shows the value represented as a horizontal bar graph. The 0-170% scale is divided into

threshold regions, from 0 to 70% value is represented by the green area, the level 70-100% by a yellow area

and 100-170% by a red area. The measured value is also shown within the display.

Jitter – Measured Jitter using selected High Pass Filter

Cable Loss – Shows the signal loss in dB at the frequency specified

Approx Cable – Shows the approximate cable length, assuming a continuous run of the specified

cable type selected by the user.

Source Level – Shows the calculated launch amplitude of the signal source, assuming a continuous

run of cable.

Cable Type – Shows the cable type used to make physical layer measurements and is user selectable

within CONFIG Physical Layer Settings Cable Type.

Eye Amplitude – Shows the amplitude of the eye waveform

Eye Risetime – Shows the rise time of the eye waveform

Eye Falltime – Shows the fall time of the eye waveform

Eye Rise-Fall – Shows the delta of the rise and fall time of the eye waveform

Eye Rise Overshoot – Shows the percentage of the rise time overshoot of the eye waveform

Eye Fall Overshoot – Shows the percentage of the fall time overshoot of the eye waveform

The user can set the threshold for the jitter meter within the configuration menu

CONFIG Physical Layer Settings SMPTE XXX Thresholds Jitter Level

NOTE:

Physical layer measurements can only be performed on Channel A input, so ensure that Input A is

selected on the front panel.

SDI Eye and Jitter Measurements How-to Guide

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Cable Stress Loop

To assist in checking the performance of a cable link the Cable Stress Loop can be used within the

WFM2300. This adds a simulated 20 meter length of 1694A cable between the I/O loop and can be

used in two ways.

Figure 4. Monitored signal stress loop.

A monitored signal can be input to the stress loop as shown in Figure 4 and the additional simulated

length of cable is added to the signal before it is input into SDI A. Monitoring the video session display

allows the user to check that the signal is still error free with the additional length of cable. If the signal

is producing CRC errors every second or every minute then the signal is marginal and the user needs to

investigate further using the eye and jitter displays to determine the problem. The cable type may need

to be changed or a re-clocking Distribution Amplifier (DA) may have to be inserted in the link to

guarantee performance of the signal.

NOTE:

The Video Session display will shows CRC errors that are occurring within the transmission path.

In some cases these errors may not be visible on the internal picture display or on a large picture

monitor, since they may be one pixel sparkle effects (black, or white pixel errors) as the error rate

increases. This sparkle effect will become more pronounced, until lines or parts of the line start to

drop out. Finally, there is no picture at all or the devices freezes on the last frame before loss of the

signal.

SDI Eye and Jitter Measurements How-to Guide

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The stress loop is bi-directional and can be used for input and output of SDI signal. The Test Signal

Generator or SDI output can be used to drive the stress loop as shown in Figure 5. In this case the

simulated 20 meters of Belden 1694A cable can be added to the generated SDI output and then applied

to the cable link to determine if the device at the end of the link can recover the clock and data from the

transmitted SDI signal. If the device fails to recover the signal then the stress loop can be removed and

the test signal generator output of the WFM2300 can be directly connected to the link to test the device

on a short run of cable. The user can then determine if the health of the link is suitable for the

transmission of the SDI signal or additional measures are needed to improve the signal transmission

such as changing the type of cable used or adding a re-clocking DA to the system.

Figure 5. Generator output via stress loop.

The stress loop can also add an interfering signal to the SDI signal to test the robustness of the receiver.

This can be configured in the PHY measurement menu.

SDI Eye and Jitter Measurements How-to Guide

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How to Configure SDI Stress Loop Amplitude

1. Select one of the tiles (1, 2, 3 or 4) and press the PHY button.

2. Push and Hold the PHY button to enable the menu.

3. Using the up and down arrows to navigate to SDI Stress Loop Amplitude and press right arrow to

select the sub menu as shown in Figure 6.

4. Use the General knob to change the value between 0 mv to 300 mv.

Figure 6. SDI Stress Loop Amplitude with varying amplitudes.

By changing the amplitude value of the stress loop the user can determine if the device under test fails

at some value during the test and the robustness of the link and device within the system can be

determined.

NOTE:

The stress loop interfering signal is set to a frequency of 20MHz and causes varying vertical

offset in the eye display.

−This interfering signal is not actually jitter and therefore does not produce time or phase

modulation of the SDI signal of the eye or jitter display, since the bandwidth of clock

recovery within the instrument is 3MHz for 3G-SDI, 1.5MHz for HD and 300kHz for SD,

well below the frequency band of the interfering signal.

−The interfering signal is typically converted to jitter by the slicing action of the SDI

equalizer and therefore can be useful for checking the jitter margin of a device.

The WFM2300 is able to generate a non-stress SDI test signal like color bars (75% or 100%)

that are typically use to test the transmission link. Alternatively the Pathological test signal

generated by the WFM2300 is used to stress the phase lock loop or equalizer of the receiving

device to provide additional stress to the transmission link.

SDI Eye and Jitter Measurements How-to Guide

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How to Configure Eye Measurements

1. Select one of the tiles (1, 2, 3 or 4) and press the PHY button.

2. Push and Hold the PHY button to enable the menu.

3. Using the up and down arrows to navigate to Display Type and press right arrow to select the sub

menu as shown in Figure 7.

4. Use the up and down arrows to select the Eye Display.

The Eye display provides a visual check on the characteristics of the received SDI signal and a variety

of information can be determined from the display and the measurement values.

The following displays can be used to identify common characteristics or problems with the SDI signal.

SMPTE standards provide specification for the launch amplitude of an SDI signal output from the device

Figure 7a. The test signal generator output of the WFM2300 was directly connected to the SDI A input

and direct measurements were made of the physical layer parameters in Figure 7b.

Figure 7a. Eye Launch Amplitude specifications.

Figure 7b. Generator output connected to SDI A.

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