AM7968-125DKC Advanced Micro Devices, AM7968-125DKC Datasheet - Page 71

• Manufacturer Part Number: AM7968-125DKC
• Description: TAXIchip Integrated Circuits(Transparent Asynchronous Xmitter-Receiver Interface)
• Manufacturer: Advanced Micro Devices

Figure 5-7
Figure 5-8
(1)
Note:
If the DC-coupled interconnection is longer than 3 , transmission line terminations are necessary. For this
case, the suggested configuration is shown in Figure 5-8. Note that the line termination network also provides
the desired pull-down to V CC – 2 V, sufficiently below the output LOW level of V CC – 1.8 V
For DC-coupled interconnections in which the distance between the TAXIchip set and
the optical module is less than 3 , transmission line terminations are not necessary. All
that is required is the appropriate ECL pull-down as shown in Figure 5-7
short line lengths, elimination of line reflections is not critical. However, without any
increase in complexity or power consumption, line reflections can be reduced simply by
locating the pull-down resistor, R
reduces the reflection coefficient at the end of the line, and therefore, reducing the
magnitude of the reflections.
DC-Coupled TAXl-Fiber Optic Interface (Unterminated)
DC-Coupled TAXl-Fiber Optic Interface
Note:
If the optical and TAXI power and ground planes are decoupled as shown in Chapter 6, AC coupling is always
recommended to allow for variations in power and ground plane voltages. AC coupling is discussed in
Section 5.5.2.
TAXI
TAXI
Adequate bypass capacitors have been omitted from this and the following figures to simplify the drawings.
TX
TX
+
–
+
–
L < 3 , Z
L>3 , Z0
+5 V
TAXIchip Integrated Circuits Technical Manual
R2
RE
0
R1
+5 V
R1
RE
R2
+
–
+
–
ODL
TX
ODL
TX
E
, at the end of the line instead of at the beginning. This
186
Optical Fiber
Optical Fiber
RE
R1+ R2
R1+ R2
R1R2
5R2
7.2 (Z
= Z0
= 3 V
0
)
ODL
ODL
RX
RX
+
–
+
–
L < 3 , Z
L>3 , Z0
+5 V
0
RE
(1)
R2
R1
+5 V
. On these
12330E-14
AMD
RE
12330E-15
R1
R2
TAXI
+
–
RX
+
–
TAXI
RX
67