Texas Instruments TLK1501, User Manual

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Optical Interfacing and Configuration
2-7
TLK1501 EVM Board Configuration
2.2 Optical Interfacing and Configuration
An interface between the TLK1501EVM and an optical transceiver can be
achieved in many ways, depending on the design of the optics module and its
associated interface circuitry. Direct connection is achieved only if the optical
interface supports the current mode logic levels of the TLK1501 device (VDD
– 1 V). If the optics module does not support or can not be biased to the CML
levels then ac-coupling must be used. Both ac- and dc-coupling schemes are
shown in Figure 2–5. The
Laser Module Section of the EVM is configured as
an ac-coupled optics module. The board is shipped with an ac-coupled output
and all that is required is external loopback cabling.
Figure 2–5. Optical Interface Configuration
50
Ω
TLK1501 TX
VDD
CMLDC bias levels
voltage
≈
(VDD-1 V)
Optical Module
DC Coupling
50
Ω
TLK1501 TX
VCC
Biased to CML Levels
Optical Module
AC Coupling
50
Ω
VDD
Biased to PECL Levels
50
Ω
The Laser Module Section is isolated from the rest of the board and requires
external loopback as shown in Figure 2–6. This makes for a versatile system
where the laser can be connected independently to other EVM systems.