gd16521 ETC-unknow, gd16521 Datasheet - Page 4

• Manufacturer Part Number: gd16521
• Description: Gbit/s Timing Laser Driver
• Manufacturer: ETC-unknow

Applications
Temperature Monitor
An on-chip, diode connected transistor is
used to monitor the junction temperature
in the proximity of the output stage. The
voltage at pin MTJ decreases with in-
creasing temperature, see
Figure 4. Temperature Monitor.
Figure 5. Voltage at pin MTJ versus
DC Coupling
For a compact design, pre-bias and mod-
ulation current can be DC coupled. DC
coupling is appropriate when connections
between laser driver and laser diode are
kept short (with low inductance) as
achieved, e.g. by flip-chip mounting of
the two dice in close proximity, see
Figure 10 on page
optimized for this configuration.
AC Coupling
AC coupling is recommended for the
packaged version, in particular when the
output is connected to the laser diode
through a transmission line, see
Data Sheet Rev.: 11
1. 00V
0. 90V
0. 80V
0. 75V
- 30
Temperature.
0
2k
5. The GD16521 is
VCC
VEE
MTJ
TEMP
50
Figure
Figure
100
4.
130
6.
Figure 6. AC coupled output.
Duty Cycle Adjustment
The “on-time” of the laser current (IM-pin)
can be increased up to 20% by control-
ling the voltage at the Duty input. In the
configuration in
sults in a longer on-time. The duty cycle
adjustment can be monitored using the
Mark/Space monitor outputs (MARKP/
MARKN), see
Figure 7. Duty cycle adjustment with an
Figure 8. MARKP/MARKN outputs.
DUTY
R
VEE
external resistor.
1k
Figure
GD16521
Figure
IMB
VCC
VEE
IB
MARKP
MARKP
IM
100nF
8.
7, a smaller R re-
VCC
220uH
VEE
L1
L2
VCC
220uH
L3
L4
VCC
L
L1 and L3 = Siemens Chip
Inductors (B82432A1224K).
L2 and L4 = Siemens ferrite
cores B64290-A36-X33 with
8 turns of 0.22mm Cu-Wire.
Laser Diode Slope Efficiency
Compensation
The pre-bias control loop may be used to
make a simple compensation for
changes in the slope efficiency of a laser
diode, in order to maintain a constant ex-
tinction ratio. Typically the slope effi-
ciency of the laser diode is inversely
proportional to the threshold current, as
shown in
pre-bias monitor current will compensate
changes in the threshold current of the
laser diode if it is added to the reference
voltage on pin IMC at a ratio. This ratio
may be chosen individually for the spe-
cific laser diode and is set by an external
R as shown in
Thereby the extinction ratio may be
maintained at a constant ratio. The varia-
tion of the pre-bias monitor current com-
pared to the pre-bias current is only
+/-1% over temperature and supply, en-
suring that the performance is not sacri-
ficed by changes in this ratio.
Figure 9. Laser diode characteristics
P
100nF
100nF
O
VCC
Figure 9
25W
Figure 3
below. Therefore the
25W
on
VCC
page
Page 4 of 13
3.
I
L