MDI_1+
MDI_1-
to RJ45
to PHY
1:1
System Overview
6
JAJU324B – March 2015 – Revised July 2017
翻訳版
—
最新の英語版資料
http://www-s.ti.com/sc/techlit/TIDU832
Copyright © 2015–2017, Texas Instruments Incorporated
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表
表
3. Gigabit Ethernet Standards
IEEE STANDARD
NAME
MEDIUM
IEEE 802.3ab
1000BASE-T
Twisted-pair copper cable
IEEE 802.3z
1000BASE-SX
Fiber optic cable
1000BASE-LX
Fiber optic cable
1000BASE-CX
Twinax
As previously mentioned, this TI Design uses twisted-pair copper cables as defined IEEE 802.3ab.
2.2.2
Gigabit Ethernet PHY Interfaces
2.2.2.1
Medium Dependent Interface: PHY Layer 1000BASE-T
The 1000BASE-T Physical Coding Sublayer (PCS), Physical Medium Attachment (PMA), and baseband
medium specifications are intended for users who want a 1000-Mb/s performance over balanced twisted-
pair cabling systems.
The 1000BASE-T PHY supports full-duplex baseband transmission through four pairs of minimum CAT5
balanced cables. The 1000 Mb/s is achieved by transmitting through four wires pairs, each at 250 Mb/s.
Using hybrids and cancellers enable full duplex transmission by allowing symbols to be transmitted and
received on the same wire pairs at the same time. Baseband signaling with a modulation rate of 125 MBd
is used on each of the wire pairs. The transmitted symbols are selected from a four-dimensional five-level
symbol constellation (4D-PAM5). In the absence of data, idle symbols are transmitted.
The IEEE 802.3 specifies specify that a PHY with a MDI that is not a power interface (PI) should provide
electrical isolation between the port device circuits, including frame ground (if any) and all MDI leads. This
electrical isolation shall withstand at least one of the following electrical strength tests:
•
1500 V
RMS
at 50 to 60 Hz for 60 s
•
2250-V DC for 60 s
•
A sequence of ten 2400-V impulses of alternating polarity, applied at intervals of not less than 1 s
To meet this requirement transformers are typically used for isolation. The typical transformer
configuration for 1000BASE-T can be seen in
for a one differential pair.
図
図
2. Gigabit Ethernet Transformer (One out of Four Pairs)
Depending on the PHY device, parallel termination might be needed for each of the MDI differential signal
pair. The termination impedance is typically 100
Ω
differentially. Newer devices like the DP83867IR
include integrated termination so no external termination resistors are required.
