Cyclone® V Device Handbook: Volume 1: Device Interfaces and Integration

ID 683375
Date 10/18/2023
Document Table of Contents

5.8.5. 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 82. Programmable Pre-EmphasisThis figure shows the LVDS output with pre-emphasis.

Table 51.   Intel® Quartus® Prime Software Assignment Editor—Programmable Pre-EmphasisThis table lists the assignment name for programmable pre-emphasis and its possible values in the Intel® Quartus® Prime software Assignment Editor.
Field Assignment
To tx_out
Assignment name Programmable Pre-emphasis
Allowed values 0 (disabled), 1 (enabled). Default is 1.