Altera Corporation
2–55
October 2007
Stratix II GX Device Handbook, Volume 2
Stratix II GX Transceiver Architecture Overview
to equalization, Stratix II GX devices offer an equalizer DC gain option.
There are three legal settings for DC gain. You specify the equalizer
settings (Equalization Settings and DC Gain) either through the
MegaWizard or dynamically using the dynamic reconfiguration
controller. To enable the dynamic reconfiguration controller, you first
enable the option for dynamic configuration in the ALT2GXB
MegaWizard Plug-In Manager. 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 Quartus II software. Refer to
“Introduction” on page 2–1
for more information.
The transmission line’s transfer function can be represented in the
frequency domain as a low-pass filter. Any frequency components below
the –3-dB frequency pass through with minimal losses. Frequency
components that are greater than the –3-dB frequency are attenuated.
This variation in frequency response yields data-dependant jitter and
other ISI effects. By applying equalization, the low frequency components
are attenuated. This equalizes the frequency response such that the delta
between the low frequency and high frequency components are reduced,
which in return minimizes the ISI effects from the transmission medium.
1
Stratix II GX receiver also offers the Adaptive Equalization
(AEQ) feature. If you enable this feature, the equalizer circuit
automatically selects and adjusts appropriate equalization
levels, depending on the changing link characteristics. You can
enable this feature through the dynamic reconfiguration
controller. For more information, refer to the
Stratix II GX
Dynamic Reconfiguration
chapter in volume 2 of the
Stratix II GX
Device Handbook
.
DC Coupling
A high-speed serial link can either be AC-coupled or DC-coupled,
depending on the serial protocol being implemented. While most of the
serial protocols require links to support AC-coupling, protocols like
Common Electrical I/O (CEI) optionally allow DC coupling.
In an AC coupled link, the DC blocking capacitor blocks the transmitter
DC common mode voltage (TX V
CM
). The Stratix II GX receiver buffer
allows a common mode voltage (RX V
CM
) setting of 0.85 V and 1.2 V. The
on-chip receiver termination and bias circuitry automatically restores the
selected common mode voltage. If you select external termination, you
must ensure that the link is terminated properly to the selected common
mode voltage.