Page 1
125 Megabaud Versatile Link
The Versatile Fiber Optic
Connection
Technical Data
Features
• Data Transmission at Signal
Rates of 1 to 125 MBd over
Distances of 100 Meters
• Compatible with Inexpensive, Easily Terminated
Plastic Optical Fiber, and
with Large Core Silica Fiber
• High Voltage Isolation
• Transmitter and Receiver
Application Circuit Schematics and Recommended
Board Layouts Available
• Interlocking Feature for
Single Channel or Duplex
Links, in a Vertical or
Horizontal Mount
Configuration
Applications
• Intra-System Links: Boardto-Board, Rack-to-Rack
• Telecommunications
Switching Systems
• Computer-to-Peripheral
Data Links, PC Bus
Extension
• Industrial Control
• Proprietary LANs
• Digitized Video
• Medical Instruments
• Reduction of Lightning and
Voltage Transient
Susceptibility
Description
The 125 MBd Versatile Link
(HFBR-0507 Series) is the most
cost-effective fiber-optic solution
for transmission of 125 MBd data
over 100 meters. The data link
consists of a 650 nm LED
transmitter, HFBR-15X7, and a
PIN/preamp receiver, HFBR25X6. These can be used with
low-cost plastic or silica fiber.
One mm diameter plastic fiber
provides the lowest cost solution
for distances under 25 meters.
The lower attenuation of silica
fiber allows data transmission
over longer distance, for a small
difference in cost. These components can be used for high speed
data links without the problems
common with copper wire
solutions, at a competitive cost.
The HFBR-15X7 transmitter is a
high power 650 nm LED in a low
cost plastic housing designed to
efficiently couple power into 1
mm diameter plastic optical fiber
HFBR-0507 Series
HFBR-15X7 Transmitters
HFBR-25X6 Receivers
and 200 µm Hard Clad Silica
(HCS®) fiber. With the recommended drive circuit, the LED
operates at speeds from 1-125
MBd. The HFBR-25X6 is a high
bandwidth analog receiver containing a PIN photodiode and
internal transimpedance amplifier.
With the recommended application circuit for 125 MBd
operation, the performance of the
complete data link is specified for
of 0-25 meters with plastic fiber
and 0-100 meters with 200 µm
HCS® fiber. A wide variety of
other digitizing circuits can be
combined with the HFBR-0507
Series to optimize performance
and cost at higher and lower data
rates.
HCS® is a registered trademark of Spectran Corporation.
5965-6114E (1/97)
17
Page 2
HFBR-0507 Series
125 MBd Data Link
Data link operating conditions
and performance are specified for
the HFBR-15X7 transmitter and
HFBR-25X6 receiver in the
recommended applications
circuits shown in Figure 1. This
circuit has been optimized for 125
MBd operation. The Applications
Engineering Department in the
Hewlett-Packard Optical
Communication Division is
available to assist in optimizing
link performance for higher or
lower speed operation.
Recommended Operating Conditions for the Circuits in Figures 1 and 2.
Parameter Symbol Min. Max. Unit Reference
Ambient Temperature T
Supply Voltage V
Data Input Voltage – Low V
Data Input Voltage – High V
Data Output Load R
Signaling Rate f
A
CC
IL
IH
L
S
Duty Cycle D.C. 40 60 % Note 2
070°C
+4.75 +5.25 V
V
-1.89 V
CC
V
-1.06 V
CC
-1.62 V
CC
-0.70 V
CC
45 55 Ω Note 1
1 125 MBd
Link Performance: 1-125 MBd, BER ≤ 10
-9
, under recommended operating conditions with
recommended transmit and receive application circuits.
Parameter Symbol Min.
Optical Power Budget, 1 m POF OPB
Optical Power Margin, OPM
POF
POF,20
[3]
11 16 dB Note 5,6,7
3 6 dB Note 5,6,7
Typ.
[4]
Max. Unit Condition Reference
20 m Standard POF
Link Distance with l 20 27 m
Standard 1 mm POF
Optical Power Margin, OPM
POF,25
3 6 dB Note 5,6,7
25 m Low Loss POF
Link Distance with Extra l 25 32 m
Low Loss 1 mm POF
Optical Power Budget, 1 m HCS OPB
Optical Power Margin, OPM
HCS
HCS,100
7 12 dB Note 5,6,7
3 6 dB Note 5,6,7
100 m HCS
Link Distance with HCS Cable l 100 125 m
Notes:
1. If the output of U4C in Figure 1, page 4 is transmitted via coaxial cable, terminate with a 50 Ω resistor to V
2. Run length limited code with maximum run length of 10 µs.
3. Minimum link performance is projected based on the worst case specifications of the HFBR-15X7 transmitter, HFBR-25X6 receiver,
and POF cable, and the typical performance of other components (e.g. logic gates, transistors, resistors, capacitors, quantizer,
HCS cable).
4. Typical performance is at 25°C, 125 MBd, and is measured with typical values of all circuit components.
5. Standard cable is HFBR-RXXYYY plastic optical fiber , with a maximum attenuation of 0.24 dB/m at 650 nm and NA = 0.5.
Extra low loss cable is HFBR-EXXYYY plastic optical fiber, with a maximum attenuation of 0.19 dB/m at 650 nm and NA = 0.5.
HCS cable is HFBR-H/VXXYYY glass optical fiber, with a maximum attenuation of 10 dB/km at 650 nm and NA = 0.37.
6. Optical Power Budget is the difference between the transmitter output power and the receiver sensitivity, measured after
1 meter of fiber. The minimum OPB is based on the limits of optical component performance over temperature, process, and
recommended power supply variation.
7. The Optical Power Margin is the available OPB after including the effects of attenuation and modal dispersion for the minimum
link distance: OPM = OPB - (attenuation power loss + modal dispersion power penalty). The minimum OPM is the margin
available for longterm LED LOP degradation and additional fixed passive losses (such as in-line connectors) in addition to the
minimum specified distance.
CC
- 2 V.
18
Page 3
Plastic Optical Fiber (1 mm POF) Transmitter Application Circuit:
Performance of the HFBR-15X7 transmitter in the recommended application circuit (Figure 1) for POF; 1125 MBd, 25°C.
Parameter Symbol Typical Unit Condition Note
Average Optical Power 1 mm POF P
avg
-9.7 dBm 50% Duty Note 1, Fig 3
Cycle
Average Modulated Power 1 mm POF P
Optical Rise Time (10% to 90%) t
Optical Fall Time (90% to 10%) t
High Level LED Current (On) I
Low Level LED Current (Off) I
mod
r
f
F,H
F,L
-11.3 dBm Note 2, Fig 3
2.1 ns 5 MHz
2.8 ns 5 MHz
19 mA Note 3
3 mA Note 3
Optical Overshoot - 1 mm POF 45 %
Transmitter Application Circuit I
CC
110 mA Figure 1
Current Consumption - 1 mm POF
Hard Clad Silica Fiber (200 µm HCS) Transmitter Application Circuit: Performance of
the HFBR-15X7 transmitter in the recommended application circuit (Figure 1) for HCS; 1-125 MBd, 25°C.
Parameter Symbol Typical Unit Condition Note
Average Optical Power 200 µm HCS P
Average Modulated Power 200 µm HCS P
Optical Rise Time (10% to 90%) t
Optical Fall Time (90% to 10%) t
High Level LED Current (On) I
Low Level LED Current (Off) I
avg
mod
r
f
F,H
F,L
Optical Overshoot - 200 µm HCS 30 %
Transmitter Application Circuit I
CC
Current Consumption - 200 µm HCS
-14.6 dBm 50% Duty Note 1, Fig 3
Cycle
-16.2 dBm Note 2, Fig 3
3.1 ns 5 MHz
3.4 ns 5 MHz
60 mA Note 3
6 mA Note 3
130 mA Figure 1
Notes:
1. Average optical power is measured with an average power meter at 50% duty cycle, after 1 meter of fiber.
2. To allow the LED to switch at high speeds, the recommended drive circuit modulates LED light output between two non-zero power
levels. The modulated (useful) power is the difference between the high and low level of light output power (transmitted) or input
power (received), which can be measured with an average power meter as a function of duty cycle (see Figure 3). Average Modulated
Power is defined as one half the slope of the average power versus duty cycle:
[P
@ 80% duty cycle - P
Average Modulated Power = ––——————————————————————
3. High and low level LED currents refer to the current through the HFBR-15X7 LED. The low level LED “off” current, sometimes
referred to as “hold-on” current, is prebias supplied to the LED during the off state to facilitate fast switching speeds.
avg
(2) [0.80 - 0.20]
@ 20% duty cycle]
avg
19
Page 4
Plastic and Hard Clad Silica Optical Fiber Receiver Application Circuit:
Performance
25°C unless otherwise stated.
Data Output Voltage - Low V
Data Output Voltage - High V
Receiver Sensitivity to Average P
Modulated Optical Power 1 mm POF
Receiver Sensitivity to Average P
Modulated Optical Power 200 µm HCS
Receiver Overdrive Level of Average P
Modulated Optical Power 1 mm POF
Receiver Overdrive Level of Average P
Modulated Optical Power 200 µm HCS
Receiver Application Circuit Current I
Consumption
Notes:
4. Performance in response to a signal from the HFBR-15X7 transmitter driven with the recommended circuit at 1-125 MBd over 1 meter
of HFBR-R/EXXYYY plastic optical fiber or 1 meter of HFBR-H/VXXYYY hard clad silica optical fiber.
5. Terminated through a 50 Ω resistor to VCC - 2 V.
6. If there is no input optical power to the receiver, electrical noise can result in false triggering of the receiver. In typical applications,
data encoding and error detection prevent random triggering from being interpreted as valid data. Refer to Applications Note 1066 for
design guidelines.
[4]
of the HFBR-25X6 receiver in the recommended application circuit (Figure 1); 1-125 MBd,
Parameter Symbol Typical Unit Condition Note
V
OL
OH
min
min
max
max
CC
-1.7 V RL = 50 Ω Note 5
CC
V
-0.9 V RL = 50 Ω Note 5
CC
-27.5 dBm 50% eye opening Note 2
-28.5 dBm 50% eye opening Note 2
-7.5 dBm 50% eye opening Note 2
-10.5 dBm 50% eye opening Note 2
85 mA RL = ∞ Figure 1
T
9
Q2 BASE
8
Q1 BASE
7
T
6
RX V
5
NC
4
PIN 19 10H116
3
PIN 18 10H116
2
R
1
J1
X VEE
X VCC
X VEE
L1
CB70-1812
C1
0.001
R691R7
CC
+
C20
10
C19
0.1
V
BB
R22
1K
R24
1K
MC10H116FN
18
19
15
U4C U4A U4B U3
17
C15
0.1
C18
0.1
R25
1K
R23
1K
V
BB
R5
22
Q1
BFQ52
C16
C2
0.1
Q2
BFQ52
1
U1A
2
91
R18
51
MC10H116FN MC10H116FN
0.1
R19
51
R20
12
R21
62
74ACTQ00
C17
0.1
10 14
7
4
5
3
20
2
V
CC
U5
TL431
3
R16
R17
V
CC
9
10
7
12
13
4
5
V
3V
V
51
9
8
51
3 V
+
C14
10
14
U1C
74ACTQ00
U1D
74ACTQ00
U1B
74ACTQ00
CC
BB
13
12
8
11
6
R14
1K
C3
0.1
C10
0.1
R15
1K
C13
0.1
C4
0.001
Q3
2N3904
C8*
R12
4.7
R13
4.7
C12
0.1
C11
0.1
V
BB
+
C5
10
C9
.47
1
2
3
4
C6
0.1
R8*
R9*
R10
15
ALL CAPACITOR VALUES
ARE IN MICRO FARADS,
WITH 10% TOLERANCE
(UNLESS OTHERWISE NOTED).
ALL RESISTANCES ARE IN
OHMS WITH 5% TOLERANCE
(UNLESS OTHERWISE NOTED).
8
5
HFBR-25X6
THE VALUES OF R8, R9, R11, AND
C8 ARE DIFFERENT FOR POF AND
HCS DRIVE CIRCUITS.
POF
300
R8
300
R9
1K
R11
43 pF
C8
R11*
HCS
82
82
470
120 pF
1
2
3
4
C7
0.001
8
U2
HFBR-15X7
5
TOLERANCE
1%
1%
1%
1%
Figure 1. Transmitter and Receiver Application Circuit with +5 V ECL Inputs and Outputs.
20
Page 5
120 Ω 120 Ω
+5 V ECL
SERIAL DATA
SOURCE
82 Ω
9 TX V
8 TD
7 TD
6 TX V
5 RX V
4
3 RD
2 RD
1 R
X VEE
EE
CC
CC
0.1 µF
+5 V ECL
SERIAL DATA
RECEIVER
+
5 V
–
82 Ω
82 Ω
120 Ω 120 Ω
10 µF
+
+
0.1 µF
4.7 µH
10 µF 0.1 µF
0.1 µF
82 Ω
4.7 µH
4.7 µH
Figure 2. Recommended Power Supply Filter and +5 V ECL Signal Terminations for
the Transmitter and Receiver Application Circuit of Figure 1.
FIBER-OPTIC
TRANSCEIVER
SHOWN IN
FIGURE 1
200
150
100
AVERAGE
MODULATED
50
AVERAGE POWER – µW
0
0
20 40 80 100
DUTY CYCLE – %
POWER
AVERAGE POWER,
50% DUTY CYCLE
60
Figure 3. Average Modulated Power.
21
19
17
15
13
11
OPTICAL POWER BUDGET –dB
9
30 50
10
POF
HCS
9070 130 150
110
DATA RATE – MBd
Figure 4. Typical Optical Power
Budget vs. Data Rate.
21
Page 6
125 Megabaud Versatile Link
Transmitter
HFBR-15X7 Series
Description
The HFBR-15X7 transmitters
incorporate a 650 nanometer LED
in a horizontal (HFBR-1527) or
vertical (HFBR-1537) gray
housing. The HFBR-15X7
transmitters are suitable for use
with current peaking to decrease
response time and can be used
with HFBR-25X6 receivers in data
links operating at signal rates
from 1 to 125 megabaud over 1
mm diameter plastic optical fiber
or 200 µm diameter hard clad
silica glass optical fiber. Refer to
Application Note 1066 for details
for recommended interface
circuits.
ANODE
CATHODE
GROUND
GROUND
1
2
3
4
SEE NOTE 6
Absolute Maximum Ratings
Parameter Symbol Min. Max. Unit Reference
Storage Temperature T
Operating Temperature T
S
O
Lead Soldering Temperature 260 °C Note 1
Cycle Time
Transmitter High Level Forward I
F,H
Input Current ≥ 1 MHz
Transmitter Average Forward Input Current I
Reverse Input Voltage V
F,AV
R
-40 85 °C
-40 70 °C
10 s
120 mA 50% Duty Cycle
60 mA
3V
GROUND
GROUND
CAUTION: The small junction sizes inherent to the design of this component increase the component's susceptibility to damage from electrostatic discharge (ESD). It is advised that normal static precautions be taken in
handling and assembly of this component to prevent damage and/or degradation which may be induced by
ESD.
WARNING: WHEN VIEWED UNDER SOME CONDITIONS, THE OPTICAL PORT MAY
EXPOSE THE EYE BEYOND THE MAXIMUM PERMISSIBLE EXPOSURE RECOMMENDED
IN ANSI Z136.2, 1993. UNDER MOST VIEWING CONDITIONS THERE IS NO EYE HAZARD.
22
Page 7
Electrical/Optical Characteristics 0 to 70°C, unless otherwise stated.
Parameter Symbol Min. Typ.
Transmitter Output P
T
-9.5 -7.0 -4.8 dBm I
Optical Power, 1 mm POF -10.4 -4.3 0-70°C
Transmitter Output P
T
-6.0 -3.0 -0.5 dBm I
Optical Power, 1 mm POF -6.9 -0.0 0-70°C
Transmitter Output P
-14.6 -13.0 -10.5 dBm I
T
Optical Power, -15.5 -10.0 0-70°C
200 µm HCS
Output Optical Power ∆P
®
T
Temperature Coefficient ∆T
Peak Emission Wavelength λ
PK
640 650 660 nm
Peak Wavelength ∆λ 0.12 nm/°C
Temperature Coefficient ∆T
Spectral Width FWHM 21 nm Full Width,
Forward Voltage V
Forward Voltage ∆V
F
F
1.8 2.1 2.4 V IF = 60 mA
Temperature Coefficient ∆T
Transmitter Numerical NA 0.5
Aperture
Thermal Resistance, θ
jc
Junction to Case
Reverse Input Breakdown V
BR
3.0 13 V I
Voltage
Diode Capacitance C
Unpeaked Optical Rise t
O
r
Time, 10% - 90% f = 100 kHz Note 5
Unpeaked Optical Fall t
f
Time, 90% - 10% f = 100 kHz Note 5
[2]
Max. Unit Condition Note
= 20 mA, 25°C Note 3
F,dc
= 60 mA, 25°C Note 3
F,d c
= 60 mA, 25°C Note 3
F,dc
-0.02 dB/°C
Half Maximum
-1.8 mV/°C
140 °C/W Note 4
= -10 µA
F,dc
60 pF VF = 0 V,
f = 1 MHz
12 ns IF = 60 mA Figure 1
9nsI
= 60 mA Figure 1
F
Notes:
1. 1.6 mm below seating plane.
2. Typical data is at 25°C.
3. Optical Power measured at the end of 0.5 meter of 1 mm diameter plastic or 200 µm diameter hard clad silica optical fiber with a large
area detector.
4. Typical value measured from junction to PC board solder joint for horizontal mount package, HFBR-1527. θjc is approximately 30°C/W
higher for vertical mount package, HFBR-1537.
5. Optical rise and fall times can be reduced with the appropriate driver circuit; refer to Application Note 1066.
6. Pins 5 and 8 are primarily for mounting and retaining purposes, but are electrically connected; pins 3 and 4 are electrically
unconnected. It is recommended that pins 3, 4, 5, and 8 all be connected to ground to reduce coupling of electrical noise.
7. Refer to the Versatile Link Family Fiber Optic Cable and Connectors Technical Data Sheet for cable connector options for 1 mm
plastic optical fiber and 200 µm HCS fiber.
8. The LED current peaking necessary for high frequency circuit design contributes to electromagnetic interference (EMI). Care must be
taken in circuit board layout to minimize emissions for compliance with governmental EMI emissions regulations. Refer to Application
Note 1066 for design guidelines.
23
Page 8
HP8082A
PULSE
GENERATOR
50 OHM
LOAD
RESISTOR
BCP MODEL 300
500 MHz
BANDWIDTH
SILICON
AVALANCHE
PHOTODIODE
HP54002A
50 OHM BNC
INPUT POD
HP54100A
OSCILLOSCOPE
1.2
1.0
0.8
0.6
0.4
0.2
NORMALIZED SPECTRAL OUTPUT POWER
0
630 650 670 680
620
640
WAVELENGTH (nm)
0° C
25° C
70° C
660
Figure 1. Test Circuit for Measuring
Unpeaked Rise and Fall Times.
2.4
0° C
2.2
2.0
1.8
– FORWARD VOLTAGE – V
F
V
1.6
1
I
– TRANSMITTER DRIVE CURRENT (mA)
F,DC
25° C
70° C
10 100
Figure 2. Typical Spectra Normalized
to the 25°C Peak.
0
-5
-10
-15
-20
– NORMALIZED OUTPUT POWER – dB
T
P
-25
1
I
– TRANSMITTER DRIVE CURRENT (mA)
F,DC
0° C
25° C
70° C
10 100
24
Figure 3. Typical Forward Voltage vs.
Drive Current.
Figure 4. Typical Normalized Output
Optical Power vs. Drive Current.
Page 9
125 Megabaud Versatile Link
Receiver
HFBR-25X6 Series
Description
The HFBR-25X6 receivers contain
a PIN photodiode and
transimpedance pre-amplifier
circuit in a horizontal (HFBR-
2526) or vertical (HFBR-2536)
blue housing, and are designed to
interface to 1mm diameter plastic
optical fiber or 200 µm hard clad
silica glass optical fiber. The
receivers convert a received
voltage. Follow-on circuitry can
optimize link performance for a
variety of distance and data rate
requirements. Electrical
bandwidth greater than 65 MHz
allows design of high speed data
links with plastic or hard clad
silica optical fiber. Refer to
Application Note 1066 for details
for recommended interface
circuits.
GROUND
GROUND
SEE NOTES 2, 4, 9
optical signal to an analog output
Absolute Maximum Ratings
Parameter Symbol Min. Max. Unit Reference
Storage Temperature T
Operating Temperature T
S
A
Lead Soldering Temperature 260 °C Note 1
Cycle Time
Signal Pin Voltage V
Supply Voltage V
Output Current I
O
CC
O
-40 +75 °C
0 +70 °C
10 s
-0.5 V
CC
-0.5 6.0 V
25 mA
V
4
3
2
1
V
CC
GROUND
GROUND
SIGNAL
CAUTION: The small junction sizes inherent to the design of this component increase the component's susceptibility to damage from electrostatic discharge (ESD). It is advised that normal static precautions be taken in
handling and assembly of this component to prevent damage and/or degradation which may be induced by
ESD.
25
Page 10
Electrical/Optical Characteristics 0 to 70°C; 5.25 V ≥ V
≥ 4.75 V; power supply must be filtered
CC
(see Figure 1, Note 2).
Parameter Symbol Min. Typ. Max. Unit Test Condition Note
AC Responsivity 1 mm POF R
AC Responsivity 200 µm HCS R
RMS Output Noise V
Equivalent Optical Noise Input P
P,APF
P,HCS
NO
N,RMS
1.7 3.9 6.5 mV/µW 650 nm Note 4
4.5 7.9 11.5 mV/µW
0.46 0.69 mV
RMS
Note 5
- 39 -36 dBm Note 5
Power, RMS - 1 mm POF
Equivalent Optical Noise Input P
N,RMS
-42 -40 dBm Note 5
Power, RMS - 200 µm HCS
Peak Input Optical Power - P
R
-5.8 dBm 5 ns PWD Note 6
1 mm POF
-6.4 dBm 2 ns PWD
Peak Input Optical Power - P
R
-8.8 dBm 5 ns PWD Note 6
200 µm HCS
-9.4 dBm 2 ns PWD
Output Impedance Z
DC Output Voltage V
Supply Current I
CC
Electrical Bandwidth BW
O
O
0.8 1.8 2.6 V PR = 0 µW
E
65 125 MHz -3 dB electrical
30 Ω 50 MHz Note 4
915mA
Bandwidth * Rise Time 0.41 Hz * s
Electrical Rise Time, 10-90% t
r
3.3 6.3 ns PR = -10 dBm
peak
Electrical Fall Time, 90-10% t
f
3.3 6.3 ns PR = -10 dBm
peak
Pulse Width Distortion PWD 0.4 1.0 ns PR = -10 dBm Note 7
peak
Overshoot 4 % PR = -10 dBm Note 8
peak
Notes:
1. 1.6 mm below seating plane.
2. The signal output is an emitter follower, which does not reject noise in the power supply. The power supply must be filtered as in
Figure 1.
3. Typical data are at 25°C and VCC = +5 Vdc.
4. Pin 1 should be ac coupled to a load ≥ 510 Ω with load capacitance less than 5 pF.
5. Measured with a 3 pole Bessel filter with a 75 MHz, -3dB bandwidth.
6. The maximum Peak Input Optical Power is the level at which the Pulse Width Distortion is guaranteed to be less than the PWD listed
under Test Condition. P
designing links up to 125 MBd (for both POF and HCS input conditions).
7. 10 ns pulse width, 50% duty cycle, at the 50% amplitude point of the waveform.
8. Percent overshoot is defined at:
9. Pins 5 and 8 are primarily for mounting and retaining purposes, but are electrically connected. It is recommended that these pins be
connected to ground to reduce coupling of electrical noise.
10. If there is no input optical power to the receiver (no transmitted signal) electrical noise can result in false triggering of the receiver.
In typical applications, data encoding and error detection prevent random triggering from being interpreted as valid data. Refer to
Application Note 1066 for design guidelines.
is given for PWD = 5 ns for designing links at ≤ 50 MBd operation, and also for PWD = 2 ns for
R,Max
(VPK - V
–––––––––––– × 100%
V
100%
100%
)
26
Page 11
Figure 1. Recommended Power Supply Filter Circuit.
Figure 2. Simplified Receiver Schematic.
Figure 3. Typical Pulse Width
Distortion vs. Peak Input Power.
Figure 4. Typical Output Spectral
Noise Density vs. Frequency.
Figure 5. Typical Rise and Fall Time
vs. Temperature..
27
Page 12
Versatile Link Mechanical Dimensions
HORIZONTAL MODULES
HFBR-1527
HFBR-2526
HORIZONTAL MODULES
HFBR-1537
HFBR-2526
Versatile Link Printed Circuit Board Layout Dimensions
HFBR-15X7
28
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