Altera Cyclone V Device Handbook page 301

1-14
Programmable Transmitter Analog Settings
Figure 1-10: Example of the Pre-Emphasis Effect on Signal Transmission at the Transmitter Output
Signal transmission at the transmitter output with and without applying pre-emphasis post-tap for a 3.125
Gbps signal with an alternating data pattern of five 1s and five 0s.
You can AC-couple the transmitter to a receiver. In an AC-coupled link, the AC-coupling capacitor blocks
the transmitter common-mode voltage. At the receiver end, the termination and biasing circuitry restores
the common-mode voltage level that is required by the receiver.
Figure 1-11: AC-Coupled Link with a Cyclone V Transmitter
The PCIe spec requires that you enable transmitter OCT for receiver detect operation.
Transmitter
Notes:
1. When you disable OCT, you must implement external termination and off-chip biasing circuitry to establish the required TX V
Programmable Transmitter Analog Settings
Figure 1-12: V (Differential) Signal Level
OD
Each transmit buffer has programmable pre-emphasis circuits that boost high frequencies in the transmit
data signal, which might be attenuated in the transmission media. Using pre-emphasis can maximize the
Altera Corporation
Output
Voltage
1-bit period
AC-Coupling
Capacitor
TX
+ –
V
CM
AC-Coupling
(1)
Capacitor
Single-Ended Waveform
Differential Waveform
V (Differential)
OD
=V -V
A B
VOD Differential
Peak-to-Peak
Physical Medium
RX
V
CM
Physical Medium
±V
OD
+V
OD
V (Differential)
OD
With Pre-Emphasis
Without Pre-Emphasis
Receiver
V
A
V
B
+700 mV
0 V Differential
-V
OD
-700 mV
Transceiver Architecture in Cyclone V Devices
CV-53001
2013.05.06
level.
CM
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