PCI Express Transmitter Compliance/Debug Solution

The PCI-SIG 6.0 specification introduces PAM4 signaling, designed to achieve 64GT/s while maintaining backward compatibility with NRZ signaling . The multi-level (PAM4) approach introduces new signal integrity challenges for adopters and validation teams. Tektronix's PCI Express 6.0 software reduces this new complexity by automating testing, ensuring measurement accuracy and repeatability.

Tektronix's PCE6 (Gen6) Option, PCE5 (Gen5) Option, PCE4 (Gen4) Option, and PCE3 (Gen 1/2/3) Option applications provide a comprehensive solution for PCI Express transmitter and reference clock compliance testing, as well as PCI Express device debug and validation according to PCI-SIG® specifications.

Application Areas

Tektronix provides a comprehensive solution for verifying and complying with PCI Express transmitters at both the base (silicon) and system levels, including support for CEM, U.2 and M.2 interfaces. Multiple protocols using the PCI Express physical layer, including NVMe and CXL, can take advantage of the transmitter and reference clock automation capabilities under the TekExpress software solution.

Compliance Test Analysis of TekExpress PCIe Test Selection

Tektronix's PCE3 (Gen1/2/3) Option, PCE4 (Gen4) Option, and PCE5 (Gen5) Option include the following compliance and commissioning tests and electrical verification:

• Root Complex Tx Jitter and Voltage

• Endpoint Tx jitter and voltage

• switch

• Bridge

• Insert card

• System board

• Embedded Systems

• Express Module

In PCIe Gen 1 and Gen 2, skew measurements require special attention to consistent patterns (such as K28.5, D21.5) and ensuring that each lane is tested with the same pattern starting point.

The Tektronix PCE6 (Gen6) option includes the following signal quality measurements:

• Unit Interval

• V-TX-DIFF-PP

• V-TX-EIEOS-FS

• T-TX-UTJ

• T-TX-UDJDD

• T-TX-RJ

• RLM-TX

• SNDR

• PS21 TX

• V-TX-BOOST

• T-TX-UPW-TJ

• T-TX-UPW-DJDD

• V-TX-AC-CM-PP

• V-TX-AC-CM-PP-Filtered

PCIe Gen6 has two Preshoot values ​​and one de-embeded value for each preset value, which makes the preset test algorithm more complicated. Tektronix PCE6 also comes with the Tektronix Preshoot Test Tool, which can be used by TekExpress or manually.

Tektronix Preset Test Tools

TekExpress Compliance Automation is now available for PCIe Gen 1-3 CEM and Gen 3 Base Tests through Option PCE3, Gen4 CEM and Gen4 Base Tests through Option PCE4, and Gen5 CEM and Gen5 Base Tests through Option PCE5.

The PCE3, PCE4, and PCE5 option applications are compatible with the Tektronix DPO/MSO70000 Series oscilloscopes and are designed to meet the challenges of next-generation serial data standards such as PCI Express. These oscilloscopes offer leading vertical noise performance and flat frequency response. The Tektronix DPO/MSO70000 Series oscilloscopes have been approved by the PCI-SIG for compliance testing.

TekExpress Oscilloscope Acquisition Settings

Compliance testing

PCI-SIG provides compliance testing for testing PCI Express systems and add-in cards. In order to be included in the integration list for a PCI Express system or device, the system or device must pass interoperability and compliance testing. For electrical verification, PCI-SIG uses SigTest post-capture analysis software, which uses waveforms captured by an oscilloscope connected to PCI-SIG's CBB (mainboard + plugboard) test fixture to analyze add-in cards, or systems using a CLB test fixture. Manually capturing the required waveforms and analyzing them is tedious and time-consuming, and prone to errors.

Tektronix's TekExpress automation for PCI Express transmitter compliance testing in the PCE3, PCE4 and PCE5 options reduces the testing effort and speeds up compliance testing through several unique and innovative features. These options ultimately allow testing of devices that support multiple technologies, such as add-in card devices that support NVMe, or testing through U.2 or M.2 connectors.

Tektronix's TekExpress automation software in the PCE3, PCE4 and PCE5 options can automatically cycle through the various speeds, de-emphasis and preset values ​​required for compliance testing by selecting a specific model of Tektronix AFG or AWG, GRL PCIE 3/4 controller or NI USB6501 CBB controller to control the DUT. This eliminates the error-prone problem of using manual buttons to control the DUT on CBB and CLB test fixtures.

A complete test run requires multiple waveform acquisitions on each channel at different DUT settings. The set of waveforms that need to be analyzed increases with the number of channels. Managing and storing data for analysis and future reference is an important criterion for any compliance solution. The TekExpress automation software in the PCE3, PCE4 and PCE5 options provides features to simplify the management of multiple acquired waveforms in addition to adjusting horizontal and vertical settings and acquisition depth to obtain the best signal quality for accurate analysis.

This feature uses PCI-SIG's SigTest EXE to analyze acquired waveforms, making the analysis results consistent with the SigTest post-capture analysis software used by the PCI-SIG working group for compliance testing. The TekExpress automation software in the PCE3, PCE4 and PCE5 options provides flexibility in selecting data rates, voltage swings, preset values ​​and tests to run. It also provides the option to de-embed channels and test fixture effects, providing an accurate representation of pin signals as required by the specification.

TekExpress uses PAMJET, the next generation PAM4 tool from Tektronix, for measurements. During analysis, TekExpress automatically sets up the tool according to the specification, captures the results, and reports them to the user. PAMJET also allows expert users to configure the PAMJET tool to test the DUT under non-spec settings for debugging. PAMJET introduces the Signal to Noise and Distortion Ratio (SNDR) measurement, and its measurement method has been updated to support the latest PCI Express 6.0 base specification. Instrument noise compensation is integrated to improve the accuracy of the measurement.

Selecting Measurement Categories in PAM4 Transmitter Analysis

All analysis results are compiled into PDF/HTML/CSV format reports which can include pass/fail summaries, eye diagrams, setup configurations and user comments. The content of the report can be customized to include information of interest such as additional results and custom report generation based on test name/pass/fail/equalization.

Reference Clock Testing Using TekExpress

Due to the reduced jitter limits driven by the highest data rates supported by the PCI-SIG standards, reference clock testing has gone from optional to mandatory in many designs. In addition, since dual ports (data and clock transmitter testing) are eliminated in Gen5 systems, compliance testing needs to be performed on the reference clock. The TekExpress PCIe solution now integrates the SkyWorks Clock Jitter Tool to make reference clock testing automated and hassle-free. Once the user connects the reference clock output to an oscilloscope, the TekExpress PCIe software acquires the signal, invokes the SkyWorks Clock Jitter Tool, and provides reference clock test results for Gen1 to Gen5. The Skyworks Clock Jitter Tool supports instrument noise compensation.

Switch Matrix Automation

The Switch Matrix application allows for configuration and setup of automated multi-channel tests using RF switches. This solution allows you to map multiple transmitter signals to specified inputs and forward the selected input to another relay or oscilloscope channel. Option SWX-PCE supports testing up to x12 and x16 channels using Keithley and Gigatronics switches respectively, enhancing throughput and automated test speed.

Switch Matrix Application Setup

Debug and Verification

If any part of the DUT or Add-in Card fails the compliance test, the application includes a DPOJET-based debug and analysis toolkit specifically designed for debug and verification of PCI Express interfaces.

The new jitter measurements introduced with PCIe Gen3 and Gen4 provide independent limits for data-dependent jitter (DDJ) and uncorrelated deterministic jitter (UDJDD). It is important to separate DDJ (which can be compensated for by transmitter and receiver equalization) and UDJDD (which can be caused by effects such as crosstalk and power supply noise).

In addition to the jitter measurements mentioned above, pulse width jitter (PWJ) is a new measurement to address the increase in channel loss from 8 to 16 Gb/s. The purpose of the PWJ measurement is to ensure that isolated bits meet the minimum pulse width requirements. All new jitter measurements implement Q-scale extrapolation based on the base specification. Tektronix's PCE3, PCE4, and PCE5 options provide a complete set of PCI Express 3.0, 4.0 and 5.0 base specification jitter measurements to help silicon designers verify that their silicon meets the base specification requirements.

Additionally, the base specification requirements are defined at the transmitter pins. Prior to measurement calculations, the test channel must be de-embedded. De-embedding filters can be easily created using Tektronix’s SDLA64 Serial Data Link Analysis software, then quickly entered into the PCE3 and PCE4 base specification measurement setups and saved for future use. In addition to jitter, PCE3 and PCE4 also provide voltage, package loss, and transmitter equalization measurements.

The PCE3 and PCE4 options leverage the channel modeling and receiver equalization capabilities of Tektronix SDLA64 software to support CEM measurements. Unlike other solutions, the PCE3 and PCE4 options provide complete signal visibility, showing the signal after the compliance channel is embedded and after receiver equalization is applied. Eye diagrams and measurements can be set up to visually view the results of channel embedding, CTLE application, and DFE. For example, when determining the optimal Rx equalization settings (CTLE settings and DFE tap values), the generated eye diagrams and measurements show the impact of post-processing on the acquired signal. Compliance measurements can then be made on the waveform.