Data Sheet, Rev. 1
August 2001
NetLight 2417K4A 1300 nm Laser
2.5 Gbits/s Transceiver
Multilayer construction also permits the routing of sen-
sitive signal traces away from high-level, high-speed
signal lines. To minimize the possibility of coupling
noise into the receiver section, high-level, high-speed
signals such as transmitter inputs and clock lines
should be routed as far away as possible from the
receiver pins.
Electrostatic Discharge
Caution: This device is susceptible to damage as
a result of electrostatic discharge (ESD).
Take proper precautions during both
handling and testing. Follow EIA ® Stan-
dard EIA-625.
Noise that couples into the receiver through the power
supply pins can also degrade performance. It is
recommended that a pi filter, shown in Figure 3, be
used for both the transmitter and receiver power
supplies.
Although protection circuitry is designed into the
device, take proper precautions to avoid exposure to
ESD.
Agere Systems employs a human-body model (HBM)
for ESD susceptibility testing and protection-design
evaluation. ESD voltage thresholds are dependent on
the critical parameters used to define the model. A
standard HBM (resistance = 1.5 kΩ, capacitance =
100 pF) is widely used and, therefore, can be used for
comparison purposes. The HBM ESD threshold
established for the 2417K4A transceiver is ±1000 V.
Data and Signal Detect Outputs
Due to the high switching speeds of CML outputs,
transmission line design must be used to interconnect
components. To ensure optimum signal fidelity, both
data outputs (RD+/RD–) should be terminated identi-
cally. The signal lines connecting the data outputs to
the next device should be equal in length and have
matched impedances. Controlled impedance stripline
or microstrip construction must be used to preserve the
quality of the signal into the next component and to
minimize reflections back into the receiver, which could
degrade its performance. Excessive ringing due to
reflections caused by improperly terminated signal
lines makes it difficult for the component receiving
these signals to decipher the proper logic levels and
can cause transitions to occur where none were
intended. Also, by minimizing high-frequency ringing,
possible EMI problems can be avoided.
Application Information
The 2417 receiver section is a highly sensitive fiber-
optic receiver. Although the data outputs are digital
logic levels (CML), the device should be thought of as
an analog component. When laying out system appli-
cation boards, the 2417 transceiver should receive the
same type of consideration one would give to a sensi-
tive analog component.
Printed-Wiring Board Layout Consider-
ations
The signal-detect output is positive LVTTL logic. A logic
low at this output indicates that the optical signal into
the receiver has been interrupted or that the light level
has fallen below the minimum signal-detect threshold.
This output should not be used as an error rate indica-
tor, since its switching threshold is determined only by
the magnitude of the incoming optical signal.
A fiber-optic receiver employs a very high gain, wide-
bandwidth transimpedance amplifier. This amplifier
detects and amplifies signals that are only tens of nA in
amplitude when the receiver is operating near its sensi-
tivity limit. Any unwanted signal currents that couple
into the receiver circuitry cause a decrease in the
receiver's sensitivity and can also degrade the perfor-
mance of the receiver's signal detect (SD) circuit. To
minimize the coupling of unwanted noise into the
receiver, careful attention must be given to the printed-
wiring board.
SINGLE ENDED
VOH
DATA
VOL
DIFFERENTIAL
VOH
DATA
VOL
At a minimum, a double-sided printed-wiring board
(PWB) with a large component-side ground plane
beneath the transceiver must be used. In applications
that include many other high-speed devices, a multi-
layer PWB is highly recommended. This permits the
placement of power and ground on separate layers,
which allows them to be isolated from the signal lines.
Figure 2. Data Input/Output Logic Level Definitions
Agere Systems Inc.
3
AGERE [ AGERE SYSTEMS ]
