ep3c120f780c8nes Altera Corporation, ep3c120f780c8nes Datasheet - Page 210

• Manufacturer Part Number: ep3c120f780c8nes
• Description: Cyclone Iii Device Family
• Manufacturer: Altera Corporation

High-Speed Differential Interfaces in Cyclone III Devices
Figure 8–22. The Output Signal with Pre-Emphasis
High-Speed
I/O Timing in
Cyclone III
Devices
8–20
Cyclone III Device Handbook, Volume 1
Programmable Pre-Emphasis
The programmable pre-emphasis boosts the high frequencies of the
output signal, which may be attenuated in the transmission media. It is
used to compensate the frequency-dependant attenuation of the
transmission line to maximize the data eye opening at the far-end
receiver. Without pre-emphasis, the output current is limited by the V
specification and the output impedance of the transmitter. At high
frequency, the slew rate may not be fast enough to reach full V
the next edge; this may lead to pattern dependent jitter. With
pre-emphasis, the output current is boosted momentarily during
switching to increase the output slew rate. The overshoot produced by
this extra switching current is different from the overshoot caused by
signal reflection. This overshoot happens only during switching and does
not produce ringing.
with pre-emphasis.
The pre-emphasis setting in Cyclone III devices is programmable — you
can choose to turn it ON or OFF. You may need to enable the
pre-emphasis if there is high attenuation in the transmission line.
This section discusses the timing budget, waveforms, and specifications
for source-synchronous signaling in Cyclone III devices. LVDS, RSDS,
mini-LVDS, PPDS, and LVEPCL I/O standards enable high-speed data
transmission. Timing for these high-speed signals is based on skew
between the data and clock signals.
High-speed differential data transmission requires timing parameters
provided by integrated circuit (IC) vendors and requires consideration of
board skew, cable skew, and clock jitter. This section provides details on
high-speed I/O standards timing parameters in Cyclone III devices.
V
V
A
B
Undershoot
Figure 8–22
Overshoot
V
OD
shows the differential output signal
Altera Corporation-Preliminary
March 2007
OD
before
OD