10 Gbit/s
Modulator Driver
GD19901
Preliminary
General Description
The GD19901 is a high-speed amplifier,
which provides a high power output drive
suitable to feed an optical modulator at
10 Gbit/s.
GD19901 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 GD19901 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 GD19901 modulator driver is deli-
vered in a 68 pin ceramic package with
50
W
transmissions lines.
Features
l
Fully differential, 6 V
PP
differential
drive capability.
CML inputs.
Limiting input stage.
Output peak-peak monitor.
Data outputs can be turned off.
Capability to AM modulate output.
Power supply: -6.5 V and +5 V
No external choke required.
Rise/fall time of maximum 45 ps
(20 – 80 %).
Power dissipation: 3.2 W (typical) at
maximum output swing.
Package: 68 pin MLC
l
l
l
l
l
l
l
l
l
VSET
l
VMONREF
VMON
Applications
VIN
VOUT
l
Telecommunications transmission
systems:
– SDH STM-64
– SONET OC-192
WDM applications.
10 Gbit/s optical transmission.
VINN
VOUTN
VEE
VCC
l
l
ISET2
Data Sheet Rev.: 08
ISET1
Functional Details
General
The GD19901 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 modulate an external optical EA
laser or to drive III-V modulator 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 is adjusted be-
tween maximum and minimum values
over a wide temperature and operat-
ing range.
The amplitude is controlled by a DC
current.
The output regulation can be dis-
abled, i.e., a fixed maximum output is
obtained (if required) by grounding
VSET and disconnecting the ISET
terminals.
4.
Output data is shutdown when the
amplitude control current and AM
control current are set to 0. The resid-
ual output data amplitude rms should
be within 1.5 % of full amplitude.
Functionality
The GD19901 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 2
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.
Vout [Vpp]
4
3,5
3
2,5
2
1,5
1
0,5
0
0
5
10
15
Iset [mA]
20
25
30
Figure 2.
VOUT vs. ISET (Typical).
0,4
Vmon - Vmonref [V]
0,3
0,2
0,1
0
0
0,5
1
1,5
2
2,5
3
3,5
Vout [Vpp]
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 0.11 V/V.
Please observe that this relation is only
valid with input signals levels within the
specified range.
Figure 3
shows a typical
measurement of VMON – VMONREF vs.
VOUT.
VCC VEE
+5V -6.5V
Special Precautions
50W
VIN
VOUT
GD16555B
MUX/PLL
50W
GD19901
VINN
VOUTN
Modulator
or
EA Laser
When the GD19901 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.
50W
VSET
VMON
VMONREF
*
: Optional
Iam
Iamp
*
FEB
*
*
ISET1
ISET2
FEB = Ferrite Bead
Figure 1.
Application Diagram
Data Sheet Rev.: 08
GD19901
Page 2 of 6
Maximum Ratings
These are the limits beyond which the component may be damaged.
All voltages in the table are referred to GND.
All currents in the table are defined positive out of the pin.
Symbol:
V
CC
V
EE
V
I
VIN,VINN
V
VSET
V
ISET
I
SET
T
0
T
S
Note 1:
Note 2:
Note 3:
Characteristic:
Positive Supply
Negative Supply
CML Input Voltage
VSET Voltage Level
Voltage @ ISET pin
Amplitude Control Current Level
Operating Temperature
Storage Temperature
Note 1
Note 3
Note 2
Conditions:
MIN.:
GND
-7.5
-3.5
V
EE
V
EE
0
0
-65
TYP.:
MAX.:
6.0
GND
0.5
GND
V
EE
+3.8
-30
70
125
UNIT:
V
V
V
V
V
mA
°C
°C
I
SET
pins are intended for current drive only. Voltage forcing into I
SET
pins that exceeds maximum ratings will cause
permanent damage to the device.
Hot-spot temperature 150
°C
@ 70
°C
T
CASE
.
ISET = ISET1 + ISET2
DC Characteristics
T
CASE
= 0
°C
to 70
°C,
VCC = +5.0 V
±
5 %, VEE = -6.5 V
±
5 %.
All voltages in the table are referenced to GND.
Symbol:
V
CC
V
EE
I
CC
I
EE
P
diss
Characteristic:
Positive Supply
Negative Supply
Positive Supply Current
Negative Supply Current
Power Dissipation
3.2
Conditions:
MIN.:
4.75
-6.8
TYP.:
5
-6.5
MAX.:
5.25
-6.2
150
-500
4.2
UNIT:
V
V
mA
mA
W
AC Characteristics
T
CASE
= 0
°C
to 70
°C,
VCC = +5.0 V
±5
%, VEE = -6.5 V
±5
%.
Symbol:
V
VOUT,VOUTN
V
VIN,VINN
t
RISE
/t
FALL
IN
t
RISE
/t
FALL
OUT
S11
S22
Note 1:
Characteristic:
Output Data Amplitude per Output
Input Data Amplitude per Input
Input Data Rise/Fall Time, 20 – 80 %
Output Data Rise/Fall Time, 20 – 80 %
0 - 6 GHz
6 - 10 GHz
0 - 6 GHz
6 - 10 GHz
t
RISE
/t
FALL
IN
Note 1
Note 1
45
-7
-5
-7
-5
300
Conditions:
MIN.:
TYP.:
3.0
400
500
40
MAX.:
UNIT:
V
PP
mV
PP
ps
ps
dB
dB
dB
dB
Measured on GD19901-68BA (gullwings) on FR4 PCB, GD99901.
Data Sheet Rev.: 08
GD19901
Page 4 of 6
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