4 Compliance Setting Fine Tuning

The most common failure with a redriver at compliance testing is the Tx Preset testing. As shown in Section 3, using a linear redriver alters the calculated Preshoot and De-Emphasis values by up to 1 dB. If the system test partner is already close to the PCIe limit for this specification, adding an improperly tuned redriver may result in a marginal failure. Similarly, adding a well equalized redriver to an endpoint that is marginal or fails the preset test can help the endpoint to pass the preset test. To properly tune the redriver, it is important to understand the core electrical concepts that impact the redriver’s performance, as described in Section 3.

To understand the redriver’s potential impact in a system, tuning typically begins with an equalization value (EQ Index) of 0 and a DC Gain of 0dB. The EQ Index can be increased one step at a time while using an eye opening monitoring tool to analyze the impact of higher equalization settings on system performance.