Transmitter Output Buffer - Altera Cyclone IV Device Handbook

1–10

Transmitter Output Buffer

Figure 1–11
Figure 1–11. Transmitter Output Buffer Block Diagram
Note to
(1) Receiver detect function is specific for PCIe protocol implementation only. For more information, refer to
Express (PIPE) Mode" on page
The Cyclone IV GX transmitter output buffers support the 1.5-V PCML I/O standard
and are powered by VCCH_GXB power pins with 2.5-V supply. The 2.5-V supply on
VCCH_GXB pins are regulated internally to 1.5-V for the transmitter output buffers. The
transmitter output buffers support the following additional features:
■ Programmable differential output voltage (V
1200 mV to handle different trace lengths, various backplanes, and various
receiver requirements.
Programmable pre-emphasis—boosts high-frequency components in the
■
transmitted signal to maximize the data eye opening at the far-end. The
high-frequency components might be attenuated in the transmission media due to
data-dependent jitter and intersymbol interference (ISI) effects. The requirement
for pre-emphasis increases as the data rates through legacy backplanes increase.
■ Programmable differential on-chip termination (OCT)—provides calibrated OCT
at differential 100  or 150 with on-chip transmitter common mode voltage
(V
termination.
1 Disable OCT to use external termination if the link requires a 85  termination, such
as when you are interfacing with certain PCIe Gen1 or Gen2 capable devices.
f
The Cyclone IV GX transmitter output buffers are current-mode drivers. The resulting
V
OD
supported V
Cyclone IV Device Handbook,
Volume 2
shows the transmitter output buffer block diagram.
Programmable
Pre-emphasis
and V
OD
Figure 1–11:
1–52.
) at 0.65 V. V is tri-stated when you disable the OCT to use external
CM CM
voltage is therefore a function of the transmitter termination value. For lists of
settings, refer to the
OD
Chapter 1: Cyclone IV Transceivers Architecture
50 or 75 
+ V -
CM
50 or 75 
Receiver
Detect (1)
)—customizes the V
OD
Cyclone IV Device Data Sheet.
Transmitter Channel Datapath
GXB_TXp
GXB_TXn
"PCI
up to
OD
February 2015 Altera Corporation