Intel® MAX® 10 General Purpose I/O User Guide

ID 683751
Date 1/27/2022

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Document Table of Contents Programmable Pre-Emphasis

The differential output voltage (VOD) setting and the output impedance of the driver set the output current limit of a high-speed transmission signal. At a high frequency, the slew rate may not be fast enough to reach the full VOD level before the next edge, producing pattern-dependent jitter. Pre-emphasis momentarily boosts the output current during switching to increase the output slew rate.

Pre-emphasis increases the amplitude of the high-frequency component of the output signal. This increase compensates for the frequency-dependent attenuation along the transmission line.

The overshoot introduced by the extra current occurs only during change of state switching. This overshoot increases the output slew rate but does not ring, unlike the overshoot caused by signal reflection. The amount of pre-emphasis required depends on the attenuation of the high-frequency component along the transmission line.

Figure 7. LVDS Output with Programmable Pre-Emphasis

Table 10.   Intel® Quartus® Prime Software Assignment for Programmable Pre-Emphasis
Field Assignment
To tx_out
Assignment name Programmable Pre-emphasis
Allowed values 0 (disabled), 1 (enabled). Default is 1.

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