3.1.1 Transmit Emphasis and DC Amplitude

Transmit emphasis and DC amplitude settings adjust the transmitter output drivers. The settings are provided from a drop-down menu of pre-defined combinations of Tx emphasis and DC amplitude.

The DC amplitude is adjusted by changing the driver segments to deliver a differential swing to the receiving device. The trade-off between large output-swing is power consumption and output return loss. The transmit emphasis adjusts the magnitude of the output based on the prior bit values reducing the successive bits. This transition emphasis compensates for the channel losses and opens the signal eye at the far-end receiver. This is accomplished by deemphasizing or weighting driver taps with negative dB adjustment.

Adjustment of the Tx amplitude and Tx emphasis are used to match the PCB interconnect losses. For information about Predefined Transmit Emphasis and DC Amplitude settings, see AC483: PolarFire FPGA Transceiver Signal Integrity Application Note.