Making New PCIe 6.0 Transmitter Equalization Measurements with Your Oscilloscope

Figure 1. Transmitter equalization test results for preset Q1.

PCI Express® 6.0 achieves its 64-GT/s data rate, double that of PCIe® 5.0, by moving from non-return-to-zero (NRZ) signaling to four-level pulse-amplitude-modulation (PAM4) signaling. This results in the need for more complex algorithms for voltage and timing measurements.

The latest release of SDAIII software for Teledyne LeCroy oscilloscopes lets you easily measure response at different transmitter equalization presets to confirm that Tx EQ is achieving the specified levels prior to taking your DUT for compliance testing. The Tx EQ measurement feature works with NRZ signals and, if you have the additional SDAIII-PAMx option, with PAM3 and PAM4 signals, too.

Transmitter Equalization Coefficients and Presets Measurement

In PCIe 6.0, transmitter equalization measurements are performed on the new PAM4 Compliance Pattern signal using the AC method that was first introduced in PCIe 5.0.

Get Ready for PCIe 6.0 Base Tx Testing--Compliance, Jitter and Eye Diagrams

Figure 1. The four levels and three eyes of the
PCIe 6.0 PAM4 signal.
Click on any image to enlarge.

The PCI Express® 6.0 Base specification was officially released in January 2022 at version 1.0, meaning it is considered final. The CEM and PHY test specifications are currently at version 0.3, and 0.5 versions of both will probably be released sometime in the third or fourth quarter of 2022. As both the CEM and PHY test specifications are still at an early stage, it's hard to predict exactly when the PCIe® 6.0 compliance test program will start, but it's safe to say it is at least a few years out. However, PCIe 6.0 Base testing is upon us, especially those of us working on chip design.

So, what can implementers expect as they retool for PCIe 6.0 Base Tx and Base Rx physical layer testing?

Automotive Ethernet in the Vehicle

Figure 1 Block diagram of a typical ADAS system
showing the in-vehicle networks used.

As all Automotive Ethernet technologies utilize a single twisted-pair cable (T1) and a point-to-point network topology, they differ primarily in their data rates and encoding methods. For the most part, the data rate determines the applications for which a particular Automotive Ethernet standard can be used. If we take the case of an automatic driver assistance system (ADAS), we can see where each Automotive Ethernet variant might best be used to replace existing automotive protocols. 

(Click on any figure to enlarge the image.)

Fundamentals of Automotive Ethernet

Figure 1: Automotive Ethernet is designed to support
increasingly complex vehicle electronic systems.

When we speak of “Automotive Ethernet”, we’re referring to a group of Ethernet interfaces intended for in-vehicle use, customized to meet the needs of the automotive industry. The first Automotive Ethernet standard was defined by Broadcom in 2011 with BroadR-Reach. Since then, IEEE has released standards for 100Base-T1, 1000Base-T1, 10Base-T1S and most recently MultiGBase-T1. Together, these standards define the general technology known as Automotive Ethernet.

Probably the first question you ask is, “Why not just use standard Ethernet?” A summary of the fundamental features of Automotive Ethernet will show how much better Automotive Ethernet is than standard Ethernet at meeting the industry’s demand for a higher speed, robust, lightweight and lower cost data interface, one that can ultimately replace the many other protocols currently used throughout the vehicle.

The Periodic Table of Oscilloscope Tools: Analyze (Part III)

We're nearing the end of our tour of the Periodic Table of Oscilloscope Tools, our way of presenting our broad palette of oscilloscope tools in a concise, clear fashion. In this installment, we'll finish up the Analyze grouping, by far the largest on the Periodic Table.

Test Challenges for PAM4 Signals

The major test challenges posed by PAM4 signals

PAM4 encoding offers the advantage of doubling the bit rate in a serial data channel, doing so by increasing the number of voltage levels from two to four. It's a fairly complex modulation scheme, so it should be no surprise that it presents some test and measurement challenges.

PAM4 Test Setups Vary With Applications

Figure 1: A high-level view of PAM4 use cases

In an earlier post, we surveyed the basic properties of PAM4 signals. Now, we will examine some of the ways in which PAM4 is finding application in the real world and what test and measurement setups might look like for those applications.

The Fundamentals of PAM4

PAM4 doubles the number of bits in serial data transmissions
by increasing the number of levels of pulse-amplitude modulation,
but does so at the cost of noise susceptibility

As our society's hunger for data grows—not only more data, but more data delivered faster—older modulation schemes based on NRZ-type encoding grow increasingly inadequate. We need to get data from point A to point B as efficiently as possible, whether that means between chips on a PC board or from one end of a long-haul optical fiber to the other. A modulation scheme that's gaining favor in many quarters is PAM4, and in this post we'll look at the basics of PAM4 before turning to the test and analysis challenges it poses.