EP2AGX95EF29C6N Datasheet, PDF (256/380 Pages) Altera Corporation – Device Interfaces and Integration

8–10
Chapter 8: High-Speed Differential I/O Interfaces and DPA in Arria II Devices
Differential Transmitter
Programmable Pre-Emphasis and Programmable V_OD.
Pre-emphasis increases the amplitude of the high frequency component of the output
signal, which helps to compensate for the frequency-dependent attenuation along the
transmission line. Figure 8–7 shows the LVDS output single-ended waveform with
and without pre-emphasis. The definition of V_OD is also shown.
Figure 8–7. LVDS Output Single-Ended Waveform with and without Programmable Pre-Emphasis (Note 1)
OUT
V_OD
OUT
Without Programmable Pre-emphasis
OUT
OUT
V_P
V_OD
V_P
Note to Figure 8–7:
(1) V_P– voltage boost from pre-emphasis.
With Programmable Pre-emphasis
Pre-emphasis is an important feature for high-speed transmission. Without
pre-emphasis, the output current is limited by the V_OD setting and the output
impedance of the driver. At high frequency, the slew rate may not be fast enough to
reach the full V_OD before the next edge, producing a pattern-dependent jitter. With
pre-emphasis, the output current is boosted momentarily during switching to increase
the output slew rate. The overshoot introduced by the extra current happens only
during switching and does not ring, unlike the overshoot caused by signal reflection.
This overshoot must not be included in the V_OD voltage.
Table 8–5 lists the assignment name and its possible values for programmable
pre-emphasis in the Quartus II software Assignment Editor.
Table 8–5. Programmable Pre-Emphasis Settings in Quartus II Software Assignment Editor
Assignment Name
Programmable Pre-Emphasis
Assignment Value
Arria II GX Device
0 (off), 1 (default on)
Arria II GZ Device
0 (default zero),
1 (medium low),
2 (medium high),
3 (high)
Arria II Device Handbook Volume 1: Device Interfaces and Integration
July 2012 Altera Corporation