Stratix V Device Handbook: Volume 2: Transceivers

ID 683779
Date 11/23/2021
Document Table of Contents Programmable Transmitter On-Chip Termination (OCT)

Transmitter buffers include programmable on-chip differential termination of 85, 100, 120, 150 Ω or OFF, for GX channels The transmitter buffer of GT channels only supports 100 Ω differential termination, but allows for finer adjustment. The resistance is adjusted by the on-chip calibration circuit during calibration, which compensates for PVT changes. The transmitter buffers are current mode drivers. Therefore, the resultant VOD is a function of the transmitter termination value.

You can disable OCT and use external termination. If you select external termination, the transmitter common mode is tri-stated. Common mode is based on the external termination connection.