EP4CE30F29C7N Datasheet, PDF (290/488 Pages) Altera Corporation – Cyclone IV Device Handbook, Volume 1

1–10
Chapter 1: Cyclone IV Transceivers Architecture
Transmitter Channel Datapath
Transmitter Output Buffer
Figure 1–11 shows the transmitter output buffer block diagram.
Figure 1–11. Transmitter Output Buffer Block Diagram
50 or 75 
GXB_TXp
Programmable
Pre-emphasis
and V_OD
+ V_CM-
50 or 75 
GXB_TXn
Receiver
Detect (1)
Note to Figure 1–11:
(1) Receiver detect function is specific for PCIe protocol implementation only. For more information, refer to “PCI
Express (PIPE) Mode” on page 1–52.
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_OD)—customizes the V_OD up to
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_CM) at 0.65 V. V_CM is tri-stated when you disable the OCT to use external
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 voltage is therefore a function of the transmitter termination value. For lists of
supported V_OD settings, refer to the Cyclone IV Device Data Sheet.
Cyclone IV Device Handbook,
Volume 2
October 2013 Altera Corporation