10 Gbit/s
Modulator Driver
GD19903
Advance Information
General Description
The GD19903 is a high-speed amplifier,
which provides a high power output drive
suitable to feed an optical modulator at
10 Gbit/s.
GD19903 provides single-ended or differ-
ential output drive to an external modula-
tor. The outputs must be externally AC
coupled, and on-chip termination is pro-
vided to minimize reflections.
The output amplitude can be adjusted to
the required value by sourcing a DC cur-
rent into a control terminal of the device.
The data outputs can be shut down by
setting the amplitude control currents to
0. When shut down, the residual output
data amplitude will be less than 1.5 % of
maximum amplitude.
The GD19903 modulator driver provides
Amplitude Modulation
(AM) control of the
outputs of the modulator driver for control
of the modulation in Mach-Zehnder
modulators. The AM will be controlled by
inserting a dither current at up to 10 kHz
with AM amplitude of up to 10 % of the
data amplitude.
An analogue monitor output is provided
to indicate peak-peak output voltage
swing.
The GD19903 modulator driver is deli-
vered in a 68 pin ceramic package with
50
W
transmissions lines.
Features
l
Fully differential, 10 V
PP
differential
drive capability.
CML inputs.
Limiting structure.
Output peak-peak monitor.
Data outputs can be turned off.
Capability to AM modulate output.
Power supply: -8.0 V and +5 V
No external choke required.
Maximum rise/fall time of 45 ps
(20 – 80 %).
Power dissipation: 8.6 W (typical) at
maximum output swing.
Package: 68 pin MLC
l
l
l
l
l
l
l
l
l
l
VMONREF
VMON
VIN
VOUT
Applications
l
VINN
VOUTN
l
Telecommunications transmission
systems:
– SDH STM-64
– SONET OC-192
WDM applications.
10 Gbit/s optical transmission.
VEE
VCC
l
ISET2
Data Sheet Rev.: 05
ISET1
Functional Details
General
The GD19903 modulator driver incorpo-
rates a limiting amplifier and provides a
high power output.
The device performs the following
functions:
1.
High output drive capability, sufficient
to drive optical III-V modulator or an
LiNbO
3
at 9.952 Gbit/s data rate.
2.
On chip termination (50
W
to ground)
on the differential CML inputs.
Outputs must be externally AC cou-
pled and on-chip termination is pro-
vided to minimize reflections.
3.
The output amplitude can be adjusted
between maximum and minimum
values over a wide temperature and
operating range.
The amplitude can be controlled by a
DC current.
4.
Shutdown of output data takes place
when the amplitude control current
and AM control current are set to 0.
The residual output data amplitude
rms is within 1.5% of full amplitude.
Functionality
The GD19903 can be driven with a single
ended or a differential input. The unused
input does not need to be terminated, but
a 50
W
resistor AC coupled to GND is
recommended. The inputs can be DC
coupled, but then the applied circuit must
not alter the quiescent input voltage. The
DC level at the output vary with the out-
put voltage swing and therefore AC cou-
pling is recommended. When used to
drive a single ended load, the unused
output shall be 50
W
terminated via an
AC coupling capacitor. (See
Figure 1
)
The amplifier output voltage swing is
controlled through the current flowing into
the pins ISET1 and ISET2. It is recom-
mended that the two pins are tied to-
gether giving a common impedance of
typical 45
W.
Figure 3
shows a typical
measurement of VOUT vs. ISET = ISET1
+ ISET2. The slope is 0.12 V/mA.
If the two ISET pins are both left open
and the Vset pin is connected to GND
maximum output voltage swing is
achieved. This setting is only recom-
mended for test purposes and VSET in-
put shall normally be left open with a
capacitor to GND. Shutting the outputs
off can be obtained by tying both ISET1
and ISET2 to VEE.
VCC VEE
+5V -8.0V
6
5
Vout [V]
4
3
2
1
0
0
5
10
15
20
Iset [mA]
25
30
35
40
Figure 2.
VOUT vs. ISET (Typical).
0,25
Vmon - Vmonref [V]
0,2
0,15
0,1
0,05
0
0
1
2
3
Vout [Vpp]
4
5
6
Figure 3.
VMON - VMONREF vs. VOUT
(Typical).
The voltage difference between Vmon
and Vmonref is a measure of the driver
output level with a slope of 37 mV/V.
Please observe that this relation is only
valid with input signals levels within the
specified range.
Figure 2
shows a typical
measurement of VMON – VMONREF vs.
VOUT
50W
VIN
VOUT
Modulator
Special Precautions
When the GD19903 is used to drive a
single-ended load, the unused output
shall be terminated (AC coupled) to
50
W.
Inputs VIN/VINN are open circuit and
short circuit (to ground) protected.
Outputs VOUT/VOUTN are open circuit
protected only. AC short circuit is
allowed.
Note:
DC short circuit to ground will
cause permanent damage to
the device.
GD16555A
MUX/PLL
50W
GD19903
VINN
VOUTN
50W
VMON
VMONREF
Iam
Iamp
FEB
ISET1
ISET2
FEB = Ferrite Bead
Figure 1.
Application Diagram
Data Sheet Rev.: 05
GD19903
Page 2 of 7
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