ADN2843CHIPSET-B Analog Devices Inc, ADN2843CHIPSET-B Datasheet - Page 6

• Manufacturer Part Number: ADN2843CHIPSET-B
• Description: IC CHIPSET LDD DUAL LOOP BAREDIE
• Manufacturer: Analog Devices Inc
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of ADN2843CHIPSET-B

• Rohs Status: RoHS non-compliant
• Data Rate: 10.709Gbps
• Number Of Channels: 1
• Voltage - Supply: 3 V ~ 3.6 V
• Current - Modulation: 80mA
• Current - Bias: 80mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: DICE
• Mounting Type: Surface Mount

ADN2843
GENERAL
Laser diodes have current-in to light-out transfer functions as
shown in Figure 1. Two key characteristics of this transfer function
are the threshold current, I
beyond the threshold current, referred to as the slope efficiency, LI.
CONTROL
A monitor photodiode, MPD, is required to control the LD. The
MPD current is fed into the ADN2843 to control the power
and extinction ratio, continuously adjusting the bias current and
modulation current in response to the laser’s changing threshold
current and light-to-current slope efficiency.
The ADN2843 uses automatic power control, APC, to maintain
a constant average power over time and temperature.
The ADN2843 uses closed-loop extinction ratio control to allow
optimum setting of the extinction ratio for every device. Thus,
SONET/SDH interface standards can be met over device variation,
temperature, and laser aging. Closed-loop modulation control
eliminates the need to either overmodulate the LD or include
external components for temperature compensation, thus reducing
research and development time and second sourcing issues.
The ADN2843 dual-loop control has two modes of operation.
Each mode is given by the configuration of the MODE and
D_IMOD pins as shown below.
Operation
Mode
A
B
Configuring the ADN2843 in Mode A or Mode B (see Figures 3
and 4) enables users to achieve accurate control of the extinc-
tion ratio. Mode B is suitable for applications where an IBIAS
pin is not available to the TOSA, or where there is no space
on the TOSA for an IBIAS inductor. Experimental data and
simulation for typical lasers has shown ER to be 0.3 dB to 0.5 dB
better in Mode A, at a 5 dB extinction ratio. Care should be
taken to ensure that the extra capacitance on the I
due to the D_IMOD connection does not degrade the eye
quality. When physical constraints do not allow a low capaci-
tance interconnect between D_IMOD and I
should be configured in Mode B (see Figure 4).
Average power and extinction ratio for both modes are set using
the PSET and ERSET pins, respectively. Potentiometers are
connected between these pins and ground. The potentiometer
R
is used to set the extinction ratio. The internal control loops
PSET
is used to set the average power. The potentiometer R
P
P1
P0
AV
Figure 1. Laser Transfer Function
MODE
Pin Setting
HIGH
LOW
ER = P1
P
AV
= P1 + P0
P0
TH
2
, and slope in the linear region
I
TH
D_IMOD
Pin Connected to
IBIAS
IBIAS_CTRL
CURRENT
I
BIAS
P
LI =
, the ADN2843
P
I
BIAS
pin
ERSET
–6–
force the PSET and ERSET pins to 1.23 V above GND. For
initial setup, R
following formulas:
The PSET resistor is given by the following formulas:
where I
The value of the ERSET resistor is a function of the operation
mode of the ADN2843 as follows:
For Mode A:
For Mode B:
Note that I
diode, therefore R
laser diode. When tuning the laser diode, R
adjusted first with R
set, R
R
Once the values R
desired average power and extinction ratio, the control loops
maintain these values of average power and extinction ratio over
environmental conditions and time.
PAVCAP AND ERCAP
The control loop constants are set by the PAVCAP and ERCAP
capacitors. The required value for the PAVCAP and ERCAP
capacitors is 22 nF.
The PAVCAP and ERCAP capacitors are connected between
the respective pins and GND. The capacitors should be low
leakage multilayer ceramic capacitors with an insulation resistance
>100 G or an RC >1000 s, whichever is lowest.
ALARMS
The ADN2843 is designed to allow 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 and FAIL. These alarms are raised
when I
olds. 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.
Example:
The laser degrade alarm, DEGRADE, is provided to give a warn-
ing of imminent laser failure if the laser diode degrades further or
if environmental conditions continue to stress the LD, such as
increasing temperature.
PSET
ERSET
is again adjusted to re-establish the desired average power.
BIAS
AV
is average MPD current.
ERSET
exceeds the respective DEGRADE and FAIL thresh-
is adjusted to set the desired extinction ratio, and
I
I
R
FAIL
ASET
PSET
ASET
and I
ERSET
PSET
R
=
and R
R
=
ERSET
=
ERSET
ERSET
50
I
PSET
1 23
100
and R
FAIL
I
R
.
and R
ASET
mA so I
PSET
ERSET
at 25 k . Once the average power is
will change from laser diode to laser
=
=
V
=
ERSET
=
R
R
PSET
50
=
1 23
PSET
PSET
may be calculated using the
100
2
.
500
DEGRADE
I
1 23
mA
AV
.
need to be adjusted for each
have been adjusted to set the
V
¥
¥
( )
=
V
ER
ER
A
W
ER
ER
500
=
=
+ 1
–
+
–
2 46
45
1
1
1
PSET
.
A
mA
k
should be
W
REV. 0