Description
Features
Category
Enables the transmitter differential pair voltages to be held
constant at the same value determined by the TX V
CM
level
with the transmitter in the high impedance state.
This feature is compliant with differential and common-mode
voltage levels and operation time requirements for transmitter
electrical idle, as specified in the PCI Express Base Specifica-
tion 2.0 for Gen1 and Gen2 signaling rates.
Transmitter
Output Tri-State
Protocol-Specific
Function
Provides link partner detection capability at the transmitter
end using an analog mechanism for the receiver detection
sequence during link initialization in the Detect state of the
PCIe Link Training and Status State Machine (LTSSM) states.
The circuit detects if there is a receiver downstream by
changing the transmitter common-mode voltage to create a
step voltage and measuring the resulting voltage rise time.
For proper functionality, the series capacitor (AC-coupled
link) and receiver termination values must comply with the
PCI Express Base Specification 2.0 for Gen1 and Gen2
signaling rates. The circuit is clocked using
fixedclk
and
requires an enabled transmitter OCT with the output tri-
stated.
Receiver Detect
Transmitter Buffer Features and Capabilities
Table 1-5: Transmitter Buffer Features
Capability
Feature
Up to 1200 mV of differential peak-to-peak output voltage
Programmable Differential Output
Voltage (V
OD
)
Support first Updated the Post Tap Pre-emphasis setting
Programmable Pre-Emphasis
0.65 V
On-Chip Biasing for Common-Mode
Voltage (TX V
CM
)
85, 100, 120, and 150 Ω
Differential OCT
Supports the electrical idle function at the transmitter as required by
the PCIe Base Specification 2.0 for Gen1 and Gen2 signaling rates
Transmitter Output Tri-State
Supports the receiver detection function as required by the PCIe Base
Specification 2.0 for Gen1 and Gen2 signaling rates
Receiver Detect
Altera Corporation
Transceiver Architecture in Cyclone V Devices
1-13
Transmitter Buffer Features and Capabilities
CV-53001
2013.05.06