PCI Express 4.0 Error Detection Using a BERT and Oscilloscope

Figure 1: BERT and Oscilloscope connection
for PCI Express 4.0 error detection.

The PCI Express® 4.0 standard specification requires an oscilloscope with at least 25 GHz analog bandwidth and a BERT which can test bit rates of at least 16 Gbps. The BERT provides a known input pattern to the PCIe® device under test (DUT), and the DUT is instructed to regenerate the identical bit pattern while placed in loopback mode. Since a BERT can output a signal when a bit error is detected, this signal can be input to the oscilloscope to trigger a synchronized capture when an error occurs. By combining the capabilities of these two instruments, a powerful combination of real-time error detection and characterization can emerge.

Connecting the Instruments

In Figure 1, a known pattern is connected from the BERT PPG D1 output to the PCIe DUT input via a 2.92 mm K-type cable. The DUT attempts to regenerate the same data pattern, while the DUT output is routed to both the BERT error detector input and the oscilloscope channel 1 via 2.92 mm K-type tables and a power splitter. An error-free reference signal is connected between the BERT D2 output to the oscilloscope channel 2, along with the error trigger signal from the error detector output to the oscilloscope channel 3. An oscilloscope Edge trigger is set on the rising edge of the error detector output signal on C3.

Gearing Up for PCIe 4.0 Electrical Compliance Test

Figure 1: A key element in PCIe 4.0
compliance test is a high-bandwidth,
real-time oscilloscope (shown is the
Teledyne LeCroy LabMaster 10Zi-A)

Armed with some of the background information and history on PCIe 4.0 electrical compliance testing, we're now ready to look at just what it takes in terms of test equipment to determine compliance for a PCIe 4.0 device. With the increase in data-transfer rate from 8 Gb/s in PCIe 3.0 to 16 Gb/s in PCIe 4.0, so too have the test equipment requirements advanced.