2.5 Gbit/s
Laser Driver
GD16575A
Preliminary
General Description
The GD16575A is a high performance
low power 2.5 Gbit/s Laser Driver.
The GD16575A is designed to meet and
exceed ITU-T STM-16 or SONET OC-48
fiberoptic communication systems re-
quirements.
The GD16575A is designed to sink a
Modulation Current into the IOUT pin and
a Pre-Bias Current into the IPRE pin. The
Modulation Current is adjustable up to
60 mA by means of the pin VMOD. The
Pre-Bias Current may be adjusted up to
50 mA by means of the VPRE pin.
A Mark-Space monitor is available on the
pins MARKP and MARKN.
The GD16575A is implemented in a Sili-
con Bipolar process and requires a single
+5 V supply or a single -5.2 V supply.
The circuit is available in a thermally
enhanced 32-pin TQFP plastic package.
Features
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Complies with ITU-T STM-16 and
SONET OC-48 standards.
Intended for driving a 50
Ω
load,
e.g. a laser diode with 50
Ω
input
impedance.
Large modulation current adjustment
range from 5 mA to 60 mA.
Output voltage over / undershoot less
than
±2
% respectively
±5
%.
Rise / fall times less than 110/100 ps.
Laser diode pre-bias adjustable up to
50 mA.
Mark-Space monitor.
Internal 50
Ω
termination of data
inputs.
Operates up to 3.5 Gbit/s.
Power dissipation: 0.38 W.
Excluding Modulation Current and
Pre-bias Current.
Silicon Bipolar process.
32 pin thermally enhanced TQFP
plastic package.
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VADJEF
VMOD
VADJBUF
VPRE
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Modulation
Current
Control
DINT
50
Pre-Bias
Current
Control
IPRE
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DIN
DINQ
50
Input
Buffer
Output
Driver
VDD
VDDCONT
IOUT
IOUTN
VEE
VEEP
VEEB
MARKP
MARKN
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DINQT
Applications
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Mark/Space
Monitor
Tele Communication:
– SDH STM-16
– SONET OC-48
Datacom up to 3.125 Gbit/s.
Electro Absorption laser driver.
Direct Modulation laser driver.
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Data Sheet Rev. 07
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Functional Details
GD16575A is a 2.5 Gbit/s laser driver. It
is capable of driving high power laser di-
odes, typically having input impedance of
50
Ω,
at a maximum modulation current
of 60 mA and a maximum pre-bias cur-
rent of 50 mA.
The differential data inputs (DINT and
DINQT) are internally terminated to the
DINT and DINQT respectively with 50
Ω
resistors. This allows loop-through termi-
nation on both inputs and ensures opti-
mum jitter performance. The input
sensitivity when driven with a single
ended signal is better than 150 mV.
The output pin (IOUT) is an open collec-
tor output designed for driving external
loads with 50
Ω
characteristic imped-
ance. Because of the nature of an open
collector the output therefore may be re-
garded as a current switch, with infinite
output impedance. The characteristic im-
pedance through the package is approxi-
mately 50
Ω.
Optimum performance of
GD16575A therefore is achieved if the
output is terminated into a 50
Ω
imped-
ance.
The output modulation current is con-
trolled by the pin VMOD and can be con-
trolled in the range from 0 mA to 60 mA,
however DC-coupling of the output is
only possible in the range from 5 mA to
40 mA. Operated with an AC-coupling,
the output modulation current can be
controlled in the range 5 mA to 60 mA.
The output voltage swing across the ex-
ternal load may be varied accordingly.
The modulation current control on pin
VMOD is implemented as a current mir-
ror and therefore sinks a current propor-
tional to the modulation current. The
current sink into the VMOD pin is ap-
proximately 3/80 of the modulation
current.
Two additional pins (VADJBUF and
VADJEF) are available in order to opti-
mise the performance of the output sig-
nal quality, specifically with respect to
overshoot and undershoot. Typically best
performance is obtained if these pins are
connected to VMOD.
The pre-bias current is controlled by the
pin VPRE and can be controlled from
0 mA to 50 mA. The pre-bias current
control on pin VPRE is implemented as a
current mirror and therefore sinks a cur-
rent proportional to the pre-bias current.
The current sink into the VPRE pin is
approximately 3/500 of the pre-bias
current.
An important parameter for laser drivers
is voltage overshoot on the output pin
(IOUT), because it determines the extinc-
tion ratio. GD16575A has been designed
with special emphasis on achieving a
very small voltage overshoot. For
GD16575A the voltage overshoot is less
than 2 % across the full modulation
Control Voltage from
Modulation Current
Control System
Control Voltage from
Pre-Bias Current
Control System
current range, when driving a 50
Ω
load.
Similarly the voltage undershoot is less
than 5 %.
A mark-space monitor is provided
through the pins MARKP and MARKN.
These may be connected as shown in
the application diagram below, with a ca-
pacitor across the two outputs and a
comparator (or Op-amp) to determine the
mark density.
AC Coupled Output
When DC coupled the output swing will
be limited by IOUT output voltage speci-
fied to -2 V. For maximum output voltage
swing the output should be AC coupled
as shown on Figure 2 or VDD should be
raised.
VDD
L1
220uH
L3
220uH
VDD
L1 and L3 = Siemens Chip
Inductors (B82432A1224K).
L2 and L4 = Siemens ferrite
cores B64290-A36-X33 with
8 turns of 0.22mm Cu-Wire.
L2
L4
100nF
100nF
50Ω
VDD
IOUT
IOUTN
Figure 2.
AC Coupled Output
VMOD / 20
VPRE / 16
Laser Diode Equivalent
50
Ω
Input Impedance
Modulation
Current
Control
100n
Pre-Bias
Current
Control
IPRE / 19
VDD
VDD
DINT / 26
50
50
Differential or
Single-ended
Data Signal
50
50
DIN / 27
Input
Buffer
Output
Driver
IOUT / 13, 14
IOUTN / 11, 12
L
C
C
50
L
VDD
50
DINQ / 30
50
100n
DINQT / 31
Mark/Space
Monitor
MARKP / 7
MARKN / 6
VDD
100n
VEEP / 18
-
+
Ref.
Negative
Supply
Figure 1.
Application Diagram
Data Sheet Rev. 07
GD16575A
Page 2 of 6
Pin List
Mnemonic:
DIN, DINQ
DINT, DINQT
IOUT, IOUTN
Pin No.:
27, 30
26, 31
14, 11
Pin Type:
AC IN
ANL IN
OPEN
COLLECTOR
OPEN
COLLECTOR
ANL IN
Description:
Data inputs. Internally terminated in 50
Ω
to DINT and DINQT
respectively.
Termination voltages for DIN and DINQ.
Laser Driver Output (2.5 Gbit/s). IOUT and IOUTN sink a modula-
tion current, which is controlled by the pin VMOD. The current into
IOUT is low when data is high on DIN.
Pre-bias current output. IPRE sinks a current, which is controlled
by the pin VPRE.
Modulation current control input. The control system is made as a
current mirror. VMOD sinks a current proportional to the modula-
tion current. This current is approximately 3/80 times “The modu-
lation current”.
Pre-bias current control input. The control system is made as a
current mirror. VPRE sinks a current proportional to the pre-bias
current. This current is approximately 3/500 times “The pre-bias
current”.
Mark-space monitor outputs. High impedance CML outputs. The
output voltage of the MARKP pin is the same polarity as the volt-
age on the DIN input.
Pins used to optimise the performance of the output in terms of
overshoot and undershoot. Typically optimum performance will be
achieved when shorted to VMOD.
Ground pins for laser driver part.
Ground pin for modulation current control system.
Negative supply pins for laser driver part.
Negative supply pin for output driver.
Negative supply pin for pre-bias circuitry.
Connect to VDD.
IPRE
VMOD
19
20
VPRE
16
ANL IN
MARKP
MARKN
VADJBUF
VADJEF
VDD
VDDCONT
VEE
VEEP
VEEB
Heat sink
7
6
22
21
2, 4, 9, 10, 12, 13,
15, 24, 28, 29
3
1, 5, 8, 23, 25, 32
18
17
Package back
ANL OUT
ANL IN
PWR
PWR
PWR
PWR
PWR
Package Pinout
DINQT
31
DINQ
DINT
VDD
VDD
VEE
32
VEE
DIN
30
29
28
27
26
25
VEE
VDD
VDDCONT
VDD
VEE
MARKN
MARKP
VEE
1
2
3
4
5
6
7
8
24
23
22
21
20
19
18
17
VDD
VEE
VADJBUF
VADJEF
VMOD
IPRE
VEEP
VEEB
10
12
13
14
15
16
11
Figure 3.
Package 32 TQFP, Top View
Data Sheet Rev. 07
GD16575A
Page 3 of 6
9
VDD
VDD
IOUTN
VDD
VDD
IOUT
VDD
VPRE
Maximum Ratings
These are the limits beyond which the component may be damaged.
All voltages in table are referred to VDD.
All currents in table are defined positive out of the pin.
Symbol:
V
EE
V
O
V
I
I
I
AC IN
I
I
VMOD
I
I
VPRE
T
O
T
S
Note 1:
Characteristic:
Power Supply
Applied Voltage (All Outputs)
Applied Voltage (All Inputs)
Input Current (AC IN)
Input Current (VMOD)
Input Current (VPRE, VADJBUF and VADJEF)
Operating Temperature
Storage Temperature
Voltage and/or current should be externally limited to specified range.
Note 1
Base
Conditions:
MIN.:
-6
V
EE
-0.5
V
EE
-0.5
-1
-4
-1
-55
-65
TYP.:
MAX.:
0
2
0.5
1
1
1
+125
+150
UNIT:
V
V
V
mA
mA
mA
°C
°C
DC Characteristics
T
CASE
= -40
°C
to 85
°C.
All voltages in table are referred to VDD.
All currents in table are defined positive out of the pin.
Symbol:
V
EE
I
EE
P
DISS
Characteristic:
Power Supply
Negative Supply Current
Power Dissipation
I
OUT
= 0 A
V
EE
=
−5.0
V,
I
OUT
= 0 A,
I
PRE
= 0 A
150
V
EE
−6
V
EE
−1
−2.0
4.0
-2.0
-50
Note 1
Note 1
Note 1, 2
-2.0
-60
-3
0
1
0
0
Conditions:
MIN.:
−5.5
TYP.:
−5.2
75
0.38
0.5
MAX.:
-4.7
UNIT:
V
mA
W
V
pp
AN IN
V
VMOD
I
VMOD
V
IN
NN
I
SINK
NN
V
LO
MARK
R
O
MARK
V
O
IPRE
I
IPRE
V
O
IOUT
I
Mod,HI
IOUT
I
Mod,LO
IOUT
Note 1:
Note 2:
Peak−peak Voltage when Input is Driven Single
V
VTH
=−1.3V
ended.
Voltage Range for VMOD
Sink Current into pin VMOD
Input Voltage Range for VPRE, VADJBUF, and
VADJEF
Sink Current into pin VPRE, VADJBUF, and
VADJEF
Low Output Voltage for Mark-Space Monitor
Output Impedance for Mark-Space Monitor
IPRE Output Voltage
IPRE Current
IOUT Output Voltage
IOUT High Modulation Current
IOUT Low Modulation Current
800
V
DD
0
V
DD
0
mV
V
mA
V
mA
V
kΩ
V
mA
V
mA
mA
R
LOAD
= 50
Ω
AC coupled to
VDD
connected to pin IOUT. Sink current is controlled by the VMOD pin, and may be
adjusted in the range as specified. Notice that high modulation current means that the output voltage level is low.
This is a leakage current. Maximum leakage current is present at maximum modulation current.
The leakage current decreases for smaller modulation currents.
Data Sheet Rev. 07
GD16575A
Page 4 of 6
AC Characteristics
T
CASE
= -40
°C
to 85
°C.
Symbol:
f
MAX
OUT
J
pp
OUT
t
RISE
OUT
t
FALL
OUT
t
OVER
OUT
t
UNDER
OUT
Note 1:
Characteristic:
Data Output Frequency
Added Output Jitter
Output Rise Time
Output Fall Time
Voltage Output Overshoot
Voltage Output Undershoot
Note 1
Note 1
Note 1
Conditions:
MIN.:
2500
20
110
100
2
5
TYP.:
MAX.:
UNIT:
Mbit/s
ps
ps
ps
%
%
R
LOAD
= 50
Ω
to
V
DD
connected to pin IOUT.
I
LD
= 40 mA. Rise/Fall times at 20 – 80 % of HI/LO voltage levels.
Package Outline
Figure 4.
Package 32L TQFP (5 x 5 x 1.4 mm)
Data Sheet Rev. 07
GD16575A
Page 5 of 6
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