PAMJET Signal Analysis of PAM4 Signal

The PAMJET Signal Analysis software application enhances the capabilities of the DPO/MSO70000DX/SX and DPO/DSA/MSO70000 series oscilloscopes (13 GHz or greater bandwidth), adding signal analysis, characterization, and compliance test for four-level Pulse Amplitude Modulation (PAMJET) devices and interfaces for both electrical and optical physical domains.

Key features

Applications

PAM4 overview

The frequency content of the NRZ signal increases linearly with bit-rate. PAM4 signaling needs half the bandwidth as NRZ for the same data rate. 400G Ethernet standards, both electrical and optical interfaces, adopted PAM4 signaling to support the forecasted growth in the datacenter and network traffic. PCI Express standards introduced PAM4 signaling in the 6.0 Base specification adding a 64GT/s line speed.

The 4 levels of PAM4 introduce additional complexity in signaling and place new demands on the test methodology. The PAM analysis PAMJET tool offers several measurement and visualization capabilities aimed at making the task of validating PAM4 designs more efficient.

PCI Express standards introduced PAM4 signaling in the 6.0 Base specification adding a 64GT/s line speed

PAM4 measurement configuration

The configuration panel is a dashboard within the PAM analysis (PAMJET) tool that enables you to configure most elements for a PAM analysis (PAMJET) run. The panel includes: measurement source selection, Clock recovery, Threshold, and Bessel-Thomson filter Equalization configuration. It also has the ability to embed or de-embed a channel using a waveform filter.

Clock recovery

Configurable PLL (phase-locked loop) clock recovery reliably extracts the symbol clock, even with highly impaired signals, uses it internally and exports the reconstructed clock waveform to a reference channel where it may be viewed.

Channel embedding / de-embedding

The waveform filter option offers the ability to embed or de-embed different channel elements. For example:

• The effects of a test fixture can be de-embedded to gain visibility of the signal at the transmitter output.
• A channel can be embedded to gain visibility of the signal at the receiver input.

You can use the Tektronix SDLA software application to further analyze and process S-parameters and create signal filters as needed, for emulation, de-embedding etc.

Equalization

It is often necessary to apply receiver equalization to open the eyes 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.

A comprehensive equalizer in the PAM analysis PAMJET tool offers the ability to do the following:

• Apply CTLE either using custom poles and zeros or standards based presets.
• Apply configurable length FFE and / or DFE with auto-adapted tap values.
• Calculate the tap values, and observe the tap values that have been calculated.

Auto configure capability

The PAM analysis PAMJET application can automatically detect the signal’s symbol rate and pattern, and choose the appropriate decision thresholds based on analysis of the eye diagram. This allows quick and error-free set-up, as well as, verifying your signal’s key characteristics.

Measurement selection

The Select panel enables you to select either electrical and optical PAM4 measurements.

The selection list allows you to choose window measurements and configure the display for ease of use and execution speed.

PAM4 measurements

The PAM analysis (PAMJET) package provides a comprehensive set of measurements that offer greater insight into signal characteristics, speeding up validation or characterization of PAM4 designs.

The supported list includes IEEE (802.3bs/802.3cd/802.3ck) and OIF-CEI Standards based measurements, SNDR and TDECQ of electrical and optical PAM4 Transmitter.

Full waveform and correlated waveform analysis

A full eye analysis can also be performed by overlaying all the unit intervals on the acquired PAM4 signal. A jitter analysis is done on the individual eyes and on the BER eye contours. Both tests can give insight into eye closure at all timing phases and reference levels simultaneously.

The correlated waveform and the correlated eye shows the signal without the random noise and jitter (and other uncorrelated components) for greater clarity of insight. The correlated waveform can be analyzed by tools and techniques similar to those found on Equivalent Time Oscilloscopes. Many performance communications standards assume access to correlated data. The PAMJET application can effectively model correlated and composite eye diagrams.

Rise and fall time analysis

Analysis of the individual transitions, rise and fall times helps separate linear impairments (bandwidth, ISI) from nonlinear (slew-rate limiting, clipping). The rise and fall times also support advanced tuning of equalization algorithms. The PAMJET software provides the max, min, and mean rise and fall time for each of the six transition types within the PAM4 eye.

Visualization

A comprehensive set of plots can be used to visualize measurement data. The plots provide additional insight into the signal characteristics and are useful for debugging.

The PAMJET toolset enables interaction with the plots and can focus in on an area of interest for closer examination and further analysis.

Error detector

The PAMJET tool comes with a built in error detector that can identify individual symbol errors in the current source waveform. The identified error can be viewed in a dedicated error navigator window.

The error navigator has several capabilities that makes it easy to quickly navigate and zoom into the error location. The additional information for the following detected errors offer help debugging symbol errors on the link:

• Location of recovered clock
• Location of symbol error reference thresholds
• Expected symbol displayed
• Actual symbol displayed

Comprehensive test report and data export

The measurement results can be saved in the form of a test report. The report includes; the configuration of the oscilloscope, application configuration, measurement results, and plots all available in an easy to read or share format.

The measurement results across multiple acquisitions can also be exported to a single CSV file for further analysis.

DPO7OE series optical probes

The DPO7OE series optical probes can be used as an optical reference receiver for high speed serial data signals (using selectable Bessel-Thomson ORR filters), or can be used as a conventional O/E converter for general wide-bandwidth optical signal acquisition. The DPO7OE series is compatible with DPO/MSO70000 C/DX/SX models. Connected to TekConnect channels provides up to 33 GHz bandwidth. Connected to ATI channels, the DPO7OE1 provides up to 42 GHz electrical response; the DPO7OE2 provides up to 59 GHz electrical bandwidth response.