2–50
Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Transmitter Modules
You specify the VOD settings either through the MegaWizard or
dynamically using the dynamic reconfiguration controller. Refer to
Programmable Pre-Emphasis
The programmable pre-emphasis module in each transmit buffer boosts
the high frequencies in the transmit data signal, which may be attenuated
in the transmission media. Using pre-emphasis can maximize the data
eye opening at the far-end receiver.
The transmission line’s transfer function can be represented in the
frequency domain as a low-pass filter. Any frequency components below
the –3dB frequency pass through with minimal losses. Frequency
components greater than the –3dB frequency are attenuated. This
variation in frequency response yields data-dependent jitter and other ISI
effects. By applying pre-emphasis, the high frequency components are
boosted, that is, pre-emphasized. Pre-emphasis equalizes the frequency
response at the receiver so the difference between the low-frequency and
high-frequency components are reduced, which minimizes the ISI effects
from the transmission medium.
The pre-emphasis requirements increase as data rates through legacy
backplanes increase. The Stratix II GX transmitter buffer employs a
pre-emphasis circuit with up to 477% of pre-emphasis to correct for losses
in the transmission medium.
You set pre-emphasis settings through a slider menu in the ALT2GXB
MegaWizard Plug-In Manager. Specify the pre-emphasis settings
(pre-emphasis control pre-tap, pre-emphasis 1st post tap, and
pre-emphasis 2nd post tap) through the MegaWizard or dynamically
using the dynamic reconfiguration controller. To enable the dynamic
reconfiguration controller, you must first enable the option for dynamic
reconfiguration in the ALT2GXB MegaWizard. After you enable that
option, you must configure the settings in the ALT2GXB_RECONFIG
MegaWizard Plug-In Manager (Stratix II GX device family) in the
information.
Programmable Transmitter Termination
The Stratix II GX transmitter buffer includes programmable on-chip
differential termination of 100
Ω, 120 Ω, or 150 Ω. The resistance is adjusted
by the on-chip calibration circuit in the calibration block (refer to
compensates for temperature, voltage, and process changes. The
Stratix II GX transmitter buffers in the transceiver are current mode