ADN2843 Analog Devices, ADN2843 Datasheet - Page 5

• Manufacturer Part Number: ADN2843
• Description: 10.7 Gbps, 3.3V Laser Diode Driver With Dual-loop Control
• Manufacturer: Analog Devices

and FAIL. These alarms are raised when IBIAS
exceeds the respective DEGRADE and FAIL
thresholds. These alarms are active high. A
resistor between ground and the ASET pin is
used to set the current at which these alarms are
raised. The current through the ASET resistor is
a ratio of 1:100 to the FAIL alarm threshold.
The DEGRADE alarm will be raised at 90% of
the FAIL threshold.
provided to give a warning of imminent laser
failure if the laser diode degrades further or
environmental conditions continue to stress the
LD, e.g. increasing temperature.
the transmitter can no longer be guaranteed to
For multi-rate operation, the LBWSET pin
should be set high and the required value for
the PAVCAP/ERCAP capacitors is 820nF.
This results in a slower loop time constant.
The PAVCAP/ERCAP capacitors are
connected between the respective pins and
GND. The capacitors should be low leakage
multi-layer ceramic capacitors with an
insulation resistance >100G or an RC
>1000s, whichever is the lower.
ALARMS
interface compliance to ITU-T-G958 (11/94)
section 10.3..1.1.2 (transmitter fail) and
section 10.3.1.1.3 (transmitter degrade).
The ADN2843 has two alarms, DEGRADE
Example:
R
The laser degrade alarm, DEGRADE, is
The laser fail alarm, FAIL, is activated when
REV. PrA 14-Jan-2002
I
The ADN2843 alarms are designed to allow
ASET
ASET
= Ibiastrip = 50mA = 500uA
= 1.23 V = 1.23 = 2.46 k
I
100
ASET
I
I
FAIL
DEGRADE
100
500uA
= 50mA so
PRELIMINARY TECHNICAL DATA
=45mA
- 5 -
be SONET/SDH compliant. This occurs when
one of the following conditions arise:
modulation and bias currents to the LD,
resulting in the MPD current dropping to zero.
This gives closed loop feedback to the system
that ALS has been enabled.
ALARM INTERFACE
- The ASET threshold is reached.
- The ALS pin is set high. This shuts off the
The alarm voltages are open collector outputs.
An internal pull up resistor of 30k is used to
pull the logic high value to VCC. However
this can be over driven with an external
resistor allowing alarm interfacing to non-
VCC levels. Non-VCC alarm output levels
must be below the VCC used for the
ADN2843.
MONITOR CURRENTS
IBMON and IMMON mirror the bias,
modulation currents at a ratio of 1:100 for
increased monitoring functionality.
IMPDMON and IMPDMON2 mirror the
current in IMPD and IMPD2 respectively with
a ratio of 1.
All monitors source current from VCC.
ID_TONE
The IDTONE pin is used for fibre
identification / supervisory channels, or for
control purposes. This pin modulates the
optical one level by adding a current to IMOD
over a possible range of 2% of min IMOD to
10% of max IMOD. The IDTONE current is
set by an external current sink connected to the
IDTONE pin. There is a gain of two between
the IDTONE pin and the IMOD current.
To ratio the IDTONE current to IMOD, the
input current can be derived from the IMMON
output current.
ADN2843