DisplayPort 2.0 Physical Layer Testing

Figure 1. Functional diagram of DisplayPort 2.0
over USB-C Source (Tx) PHY testing.

The Video Electronics Standards Association (VESA) DisplayPort 2.0 video interface introduces a new performance standard with an increase in data bandwidth of three times compared to the older DisplayPort 1.4a specification, achieved by using four lanes of  up-to-20 Gb/s data per lane. This permits display resolutions to better than 8K, higher refresh rates and better dynamic range. These advantages are available using native DisplayPort connectors as well as the USB Type-C connector, which allows devices to handle video data, USB data and power all in the same connector.

With the USB-C cable now carrying DisplayPort and lower-speed sideband data, testing for USB devices has expanded to cover many dependencies between these protocols. This series will give an overview DisplayPort 2.0 physical-layer testing and how it relates to USB testing.

Source (Tx) Test Equipment

DisplayPort 2.0 supports data rates of 10, 13.5 and 20 Gb/s. Physical-layer (PHY) compliance testing for DisplayPort 2.0 transmitters (Figure 1) requires:

• An oscilloscope
• An AUX controller
• Related cables and test fixtures

The DisplayPort 2.0 CTS requires oscilloscope bandwidths of 25 GHz for the 20 and 13.5 Gb/s data rates, while the 10Gb/s data rate relaxes the bandwidth requirement to 16 GHz. Teledyne LeCroy oscilloscopes that offer the required bandwidth are:

• LabMaster 10 Zi-A, which supports measurements on two lanes at 80 GS/s
• WaveMaster/SDA 8 Zi-B, which measures a single lane at 80 GS/s

Both support the SDAIII-CompleteLinQ Serial Data Analysis software option, which is required to display and analyze data from all four lanes simultaneously.

In addition to the oscilloscope, a plug test fixture is used to break out the signals from the DisplayPort 2.0 source port as well as the AUX data. Teledyne LeCroy recommends the Wilder Technologies DP-TPA-P plug test fixture for devices using legacy DisplayPort connectors, and the DPC-TPA-P for devices using the USB Type-C connectors.

The required "golden" test cables are high quality, low insertion loss cables phase matched to within ±5° at 40 GHz. Their insertion loss is less than 1.5 dB to 10 GHz.

An AUX controller is used to initiate test patterns for source testing when working in USB4 AUX mode. An official AUX controller for DisplayPort 2.0 is currently under development by VESA, but in the meantime, the  Wilder Technologies DUTC mode control module with a suitable cable fixture can be used.

Sink (Rx) Test Equipment

In addition to the equipment above, DisplayPort 2.0 receiver testing requires:

• A bit error rate tester (BERT) with associated modules
• An inter-symbol interference (ISI) board and receptacle test fixture
• A vector network analyzer (VNA) or WavePulser 40iX

Figure 2. Functional diagram of  DisplayPort 2.0
Sink (Rx) PHY testing.

Teledyne LeCroy recommends the Anritsu MP1900A SQA-R BERT, which provides high accuracy stressed signal generation (SSG) from 2.4 to 32.1 Gb/s with exceptionally low intrinsic jitter. It also provides jitter and noise tolerance testing with high reproducibility. The BERT requires an additional  12.5 GHz 4-port synthesizer, jitter modulation and noise generator modules, and two DC blocks.

Two, 3-port power dividers, an inter-symbol interference (ISI) board set and a receptacle test fixture (also available from Wilder Technologies) are added to the required equipment. The power dividers are used to add controlled amounts of crosstalk. The ISI boards are a set of PC boards with varying path lengths used to control the insertion loss of the total channel. The ISI boards and a set of fully characterized low-loss cables are available from Wild River technology as a loss modelling kit.

Figure 3. WavePulser 40iX measures the insertion loss
of the total channel and the DisplayPort cable.

Because insertion loss for both the total channel and the DisplayPort cable connected between the receptacle test fixtures must be within specification, all the sink test signal paths have to be carefully characterized so that the cables and fixtures can be de-embedded from the measurements. This characterization can be performed using a vector network analyzer (VNA) or the Teledyne LeCroy WavePulser 40iX High Speed Interconnect Analyzer to measure the S-parameters, especially the insertion loss, of the cables and test fixtures. 

Teledyne LeCroy’s new QualiPHY DisplayPort 2.0 software options, QPHY-DP20-Source and QPHY DP20-Sink, can be installed on the oscilloscope to automate PHY compliance testing.

Watch Mike Engbretson explain the tests in our on-demand webinar, "DisplayPort 2.0 Compliance Test Overview, Pt. 2, PHY Testing."