VSC8201DL VITESSE [Vitesse Semiconductor Corporation], VSC8201DL Datasheet - Page 7

• Manufacturer Part Number: VSC8201DL
• Description: Single Port 10/100/1000BASE-Tand 1000BASE-X PHY
• Manufacturer: VITESSE [Vitesse Semiconductor Corporation]

Design for Signal Integrity
Many high speed signal pins on the VSC8201 have rise/fall times of the order of 0.7 to 2.4 ns. Because of these fast rise/fall times, inter-
connects should be treated as transmission lines rather than simple lumped element connections. Use of transmission lines with a basic
understanding of line matching will reduce signal reflections which degrades overall performance of the part.
Theory
In order to apply correct impedance matching/termination techniques it is important to know about the types of interconnects used on the
PC board. There are 2 kinds of traces on a PC Board.
•
•
Impedance of a transmission line is determined by the relative dielectric constant
Characteristic impedance of the microstrip is calculated using the approximation:
The propagation delay for the microstrip is:
Rev. 1.6.3 - 9/29/04
h
,the width
In case the signal transmission line is sandwiched between the dielectric material of the board and 2 conducting planes it is called a
stripline.
A signal transmission line that has one side open to air and dielectric material and a conducting plane beneath it, is called a micros-
trip.
t
Z
pd
o
w
=
=
and the thickness of the transmission line .
-------------------------
(
85
ε
r
)
87
+
⋅
1.41
0.475ε
VITESSE - CONFIDENTIAL & PROPRIETARY - DO NOT COPY WITHOUT PERMISSION
⋅
ln
r
------------------- Ω
0.8w
+
5.98 h ⋅
0.67
+
Figure 6: Transmission Lines
t
ps/ft
t
ε
r
of the PC board material, thickness of the dielectric
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VSC8201DL