Intel® Agilex™ F-Series and I-Series General-Purpose I/O User Guide

ID 683780
Date 6/14/2022
Public

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7.1. Programmable Pre-Emphasis

The 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. With pre-emphasis, the output current is boosted momentarily during switching to increase the output slew rate.

Pre-emphasis increases the amplitude of the high-frequency component of the output signal and thus helps to compensate for the frequency-dependent attenuation along the transmission line. The overshoot introduced by the extra current happens only during a change of state switching to increase the output slew rate and 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 52. Programmable Pre-emphasisThis figure shows the true differential output with pre-emphasis.

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