1.1.2.3 Transmit Output Buffer

The following figure shows the transmit output buffer of the transceiver lane, which connects to the PCB through the XCVR_TXP/N output pins. The low-power H-bridge differential output buffer includes a configurable driver for amplitude on the 100Ω differential load up to a maximum swing of 1V peak to peak. In addition, selectable levels of transmit common-mode voltage (Tx VCM) are available besides the swing amplitude control for the output driver segments to control the amount of emphasis. The transmit output buffer settings are accessible in real-time for adjustment through the JTAG interface using SmartDebug. It includes a receiver detection to recognize the presence of a physical link. The output buffer also has electrical idle capabilities used to orderly quiet the link transmitters.

Transmit common-mode voltage levels for the drivers are selected by the user during the configuration of the PMA when using the transceiver configurator in the Libero software. Reducing the transmit output amplitude lowers the overall transceiver power consumption.