Optional Built-In Ac Coupling - Xilinx Virtex-5 RocketIO GTP User Manual

R
High-Pass Pole Location: RXEQPOLE[3:0]
MGTRXN
Line Termination
MGTRXP
Reference to 2/3 AVTTRX:
RCV_TERM_GND AND
RCV_TERM_VTTRX
Reference to Ground:
RCV_TERM_GND
Reference to AVTTRX:
RCV_TERM_VTTRX
AC Coupling Bypass:
AC_CAP_DIS
Notes:
1. The internal AC coupling capacitor is not a replacement for offchip coupling capacitors. It is an isolation capacitor for
nonstandard termination voltages.
2. These port names have the prefix MGT to identify them easily in a pad file that is very often used to create symbols for board
design schematics. In this document, the MGT prefix was removed from those names; however, names with and without the
MGT prefix are synonymous to each other.
The receiver includes four main features for optimizing signal integrity:
•
•
•
•

Optional Built-In AC Coupling

The GTP receiver includes small AC-coupling capacitors that isolate the receiver from the
line. These capacitors are required when the RX termination is set to GND and are enabled
by default. When GND termination is not used, these capacitors can be disabled to allow
for DC coupling or more optimal off-chip AC coupling. See
Interface,"
capacitor.
The AC_CAP_DIS attribute controls the AC-coupling bypass switch shown in
As required when built-in AC coupling is activated, RCV_TERM_MID activates the
2/3 MGTAVTTRX reference behind the built-in, AC-coupling circuit.
To turn on built-in AC coupling, AC_CAP_DIS is set to FALSE, and RCV_TERM_MID is
set to TRUE. To disable the built-in AC coupling, AC_CAP_DIS is set to TRUE, and
RCV_TERM_MID is set to FALSE.
Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
V1: 2/3 AVTTRX
V2: AVTTRX
+
V1
Figure 7-2: Receiver Channel Internal Architecture
Optional Built-In AC Coupling
Configurable Termination Impedance
Configurable Termination Voltage
Optional Configurable RX Linear Equalization
for more details about how to pick an appropriately sized external AC coupling
www.xilinx.com
RX Termination and Equalization
Single-Pole
High-Pass
Filter
High-Pass/Wideband Mixing Ratio:
RXEQMIX[1:0]
+
V2
(1)
+
V1
(1)
RCV_TERM_MID
+
_
High Pass
to
RX CDR
Wideband
+
_
V1: 2/3 AVTTRX
UG196_c7_02_030307
Chapter 10, "GTP-to-Board
Figure 7-2.
127