Data Sheet
January 2000
1340-Type Lightwave Receiver
Noise that couples into the receiver through the power
supply pins can also degrade device performance. The
application schematics, Figures 3—5, show recom-
mended power supply filtering that helps minimize
noise coupling into the receiver. The bypass capacitors
should be high-quality ceramic devices rated for RF
applications. They should be surface-mount compo-
nents placed as close as possible to the receiver power
supply pins. The ferrite bead should have as high an
impedance as possible in the frequency range that is
most likely to cause problems. This will vary for each
application and is dependent on the signaling frequen-
cies present on the application circuit card. Surface-
mount, high-impedance beads are available from sev-
eral manufacturers.
Description
(continued)
To help ensure high product reliability and customer
satisfaction, Agere is committed to an intensive quality
program that starts in the design phase and proceeds
through the manufacturing and shipping process. Opto-
electronics subsystems are qualified to Agere internal
standards using MIL-STD-883 test methods and pro-
cedures and sampling techniques consistent with
Tel-
cordia Technologies
requirements. The 1340 receiver
qualification program meets the intent of
Telcordia
Technologies
TR-NWT-000468 andTA-TSY-000983.
Application Information
The 1340 receiver is a highly sensitive fiber-optic
receiver. Although the data outputs are digital logic lev-
els (PECL), the device should be thought of as an ana-
log component. When laying out the printed-wiring
board (PWB), the 1340 receiver should be given the
same type of consideration one would give to a sensi-
tive analog component.
At a minimum, a double-sided printed-wiring board with
a large component-side ground plane beneath the
receiver must be used. In applications that include
many other high-speed devices, a multilayer PWB is
highly recommended. This permits the placement of
power and ground connections on separate layers,
which helps minimize the coupling of unwanted signal
noise into the power supplies of the receiver.
Data and Flag Outputs
The data outputs of the 1340 receiver are driven by
open-emitter NPN transistors which have an output
impedance of approximately 7
Ω.
Each output can pro-
vide approximately 50 mA maximum output current.
Due to the high switching speeds of ECL outputs,
transmission line design must be used to interconnect
components. To ensure optimum signal fidelity, both
data outputs (DATA and DATA) should be terminated
identically. The signal lines connecting the data outputs
to the next device should be equal in length and should
have matched impedances.
Controlled impedance stripline or microstrip construc-
tion must be used to preserve the quality of the signal
into the next component and to minimize reflections
back into the receiver. Excessive ringing due to reflec-
tions caused by improperly terminated signal lines
makes it difficult for the component receiving these sig-
nals to decipher the proper logic levels and may cause
transitions to occur where none were intended. Also, by
minimizing high frequency ringing due to reflections
caused by improperly designed and terminated signal
lines, possible EMI problems can be avoided. The
applications sections in the Signetics
*
ECL 10K/100K
Data Manual or the National Semiconductor
†
ECL
Logic Databook and Design Guide
provide excellent
design information on ECL interfacing.
Layout Considerations
A fiber-optic receiver employs a very high-gain, wide-
bandwidth transimpedance amplifier. The amplifier
detects and amplifies signals that are only tens of nA in
amplitude. 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 loss of signal (FLAG) circuit.
To minimize the coupling of unwanted noise into the
receiver, route high-level, high-speed signals such as
transmitter inputs and clock lines as far away as possi-
ble from the receiver pins. If this is not possible, then
the PWB layout engineer should consider interleaving
the receiver signal and flag traces with ground traces in
order to provide the required isolation.
*
Signetics
is a registered trademark of Signetics Corp.
†
National Semiconductor
is a registered trademark of National
Semiconductor Corporation.
Agere Systems Inc.
3
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