Characterization of PAM4 Signals from standards ranging from OIF-CEI-VSR-56G-PAM4 to IEEE 802.3bs CDAUI-8.
PAM4 signal modulation techniques are being adopted in the latest 400 Gigabit Ethernet standards by the IEEE P802.3bs working group for 400G (typically 8 x 52G) electrical and optical interfaces. Compared to traditional NRZ that uses two-level signaling, the four-level scheme used in PAM4 significantly increases signal complexity and places new demands on test methodology, which this PAM4 measurement package supports.
Configuring the oscilloscope for PAM-4 analysis is automatically done by the PAM4 analysis software. Simply, select the data source and clock recovery method and all measurements are automatically computed.
PAM-4 measurements can be grouped into those that are done on the entire waveform, individual eyes and transitions within the correlated waveform, and on the correlated waveform.
In addition to jitter analysis, the linearity measurement is provided to measure the distribution between the four signaling levels. This measurement is done according to the 802.3bj specification when the input signal is a specification-complaint Linearity pattern, and according to an adapted method even when the signal pattern is not complaint.
Jitter analysis is done on the individual eyes within the link. For PAM-4 this results in three sets of measurements, including TJ at 3 user specified BER, RJ(dd), DJ(dd), Eye Width and Height.
Separation of the correlated waveform and eye give you insight into how much additional eye opening is theoretically obtainable through equalization. The correlated waveform can be analyzed by tools and techniques similar to those found on Equivalent Time Scopes. Many performance communications standards assume access to correlated data, and the PAM4 Analysis application can effectively model correlated and composite eye diagrams.
Analysis of the individual transitions rise and fall times, helps separate linear impairments (bandwidth, ISI) from nonlinear (slew-rate limiting, clipping) and supports advanced tuning of equalization algorithms. PAM-4 analysis software provides the max, min, and mean rise and fall time for each of the six transition types within the PAM4 eye.
|Unit interval||Mean duration of one symbol (two bits)|
|Symbol rate / bit rate||Number of symbols or bits per second|
|Linearity (RLM)||Minimum level separation relative to peak-to-peak, expressed as a percentage|
|Level||Symbol levels: L0, L1, L2, L3|
|Rise and fall time||Rise and fall time for each transition 0->3, 0->2, 0->1, 1->2, 1->3, 2->3|
|Offset||Horizontal offset from nominal center of UI to center of actual eye opening|
|TJ||Total jitter, simultaneously at 3 user-selectable BER levels|
|RJ (dd)||Random jitter, dual dirac|
|DJ (dd)||Deterministic jitter, dual dirac|
|Eye width||Horizontal eye opening|
|Eye height||Vertical eye opening|
|EW||Eye Width at BER|
|EH||Eye Height at BER|
|VEC||Vertical Eye Closure|
|Level deviation||Level separation relative to peak-to-peak|
|Level thickness||Level RMS variation at horizontal position of minimum inter-symbol interference|
|Time deviation||Mean deviation of the horizontal minimum-ISI points, relative to the unit interval|
|Time deviation mean||Time deviation, after removal of any bias due to clock recovery skew|
|Pk-Pk||Nominal signal swing from (settled) 0 -> (settled) 3|
|Level||Symbol levels: L0, L1, L2, L3|
Link margin can be improved by de-embedding the effects of fixtures, cables, and other artifacts of the measurement circuit. In other scenarios, it is desired to model the effects of a channel using S-parameters. This is convenient for determining overall device margin across a single or multiple channels without needing physical media.
Insertion loss, return loss, and cross coupling effects can all be modeled and removed from the signal using SDLA Visualizer. SDLA Visualizer will create a filter that can be directly used within the PAM4 application.
It is often necessary to apply receiver equalization to open the eye before measurements can be performed. In most cases the lack of physical access makes it impossible to verify the receiver circuit behavior and monitor the effects of clock recovery and equalization. CTLE and DFE equalization parameters can be conveniently set directly in the PAM-4 analysis software. SDLA Visualizer also incorporates IBIS-AMI models, which provide the advantage of using silicon specific equalization algorithms that provide the greatest level of correlation between what the receiver actually sees and the simulated waveform.
Once the measurements have been computed, it is often desired to save a test report to share with others or for data archiving. The PAM-4 analysis package generates an html-style report, saved in archived format (.mht) for compactness and portability. The report includes the configuration of the oscilloscope, application configuration, measurement results, and plots.
All test configurations can be saved and recalled for later use, ensuring consistency between each test session.
For additional information we recommend the following resources: literature on the DPO/MSO70000 Series oscilloscopes, their probes and software applications; literature on SDLA Visualizer available on www.tektronix.com.
50 repeats required for jitter measurement; at least 3 repeats required for Rise/Fall Time and other correlated measurements.
CTLE: custom filter with 1 zero and 2 poles or OIF-CEI standard presets. DFE, up to 10 taps. Adaptive tap values.
The PAM4 Transmitter analysis software for Tektronix DPO/MSO70000 Win7 Series oscilloscopes
|DPO/MSO70000||PAM4||PAM4 Transmitter Analysis software|
|DPO-UP||PAM4||PAM4 Transmitter Analysis Software Upgrade|
|DPOFL PAM4||-||PAM4 Transmitter Analysis software floating license|
|DPOFT PAM4||-||PAM4 Transmitter Analysis software trial license|
SDLA Visualizer channel de-embedding, embedding, and equalization (required to use PAM4 CTLE or DFE)
CE Marking Not Applicable.
|Tektronix is registered to ISO 9001 and ISO 14001 by SRI Quality System Registrar.|
|Product(s) complies with IEEE Standard 488.1-1987, RS-232-C, and with Tektronix Standard Codes and Formats.|
Product Area Assessed: The planning, design/development and manufacture of electronic Test and Measurement instruments.
Last Modified: 2016-09-07 07:00:00