Table 1-4: Description of the Transmitter Buffer Features
Features provided by the Pseudo Current Mode Logic (PCML) output buffer to the integrated circuitry.
Description
Features
Category
Controls the current mode drivers for signal amplitude to
handle different trace lengths, various backplanes, and receiver
requirements. The actual V
OD
level is a function of the current
setting and the transmitter termination value.
Programmable
Differential
Output Voltage
(V
OD
)
Improve Signal Integrity
Boosts the high-frequency components of the transmitted
signal, which may be attenuated when propagating through
the transmission medium. The physical transmission medium
can be represented as a low-pass filter in the frequency
domain. Variation in the signal frequency response that is
caused by attenuation significantly increases the data-
dependent jitter and other intersymbol interference (ISI)
effects at the receiver end. Use the pre-emphasis feature to
maximize the data opening at the far-end receiver.
Programmable
Pre-Emphasis
Controls the rate of change for the signal transition.
Programmable
Slew Rate
Establishes the required transmitter common-mode voltage
(TX V
CM
) level at the transmitter output. The circuitry is
available only if you enable OCT. When you disable OCT,
you must implement off-chip biasing circuitry to establish
the required TX V
CM
level.
On-Chip Biasing
Save Board Space and
Cost
The termination resistance is adjusted by the calibration
circuitry, which compensates for PVT.
You can disable OCT and use external termination. However,
you must implement off-chip biasing circuitry to establish
the required TX V
CM
level. TX V
CM
is tri-stated when you
use external termination.
Differential OCT
Controls the impedance of V
CM
. A higher impedance setting
reduces current consumption from the on-chip biasing
circuitry.
Programmable
V
CM
Current
Strength
Reduce Power
Transceiver Architecture in Cyclone V Devices
Altera Corporation
CV-53001
Transmitter Buffer
1-12
2013.05.06