MAX3865 [MAXIM]
2.5Gbps Laser Driver with Automatic Modulation Control; 带有自动调制控制的2.5Gbps激光驱动器
| 型号： | MAX3865 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 2.5Gbps Laser Driver with Automatic Modulation Control |
| 文件： | 总16页 (文件大小：633K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-2247; Rev 1; 4/02
2.5Gbps Laser Driver with Automatic
Modulation Control
General Description
Features
The MAX3865 is designed for direct modulation of laser
diodes at data rates up to 2.5Gbps. It incorporates two
feedback loops, the automatic power-control (APC)
loop and the automatic modulation-control (AMC) loop,
to maintain constant average optical output and extinc-
tion ratio over temperature and laser lifetime. External
resistors or current output DACs may set the laser out-
put levels. The driver can deliver up to100mA of laser
bias current and up to 60mA laser modulation current
with a typical (20% to 80%) edge speed of 84ps.
ꢀ Single +3.3V or +5V Power Supply
ꢀ 68mA Supply Current
ꢀ Up to 2.5Gbps (NRZ) Operation
ꢀ Feedback Control for Constant Average Power
ꢀ Feedback Control for Constant Extinction Ratio
ꢀ Programmable Bias Current Up to 100mA
ꢀ Programmable Modulation Current Up to 60mA
ꢀ 84ps Rise/Fall Time
The MAX3865 accepts differential clock and data input
signals with on-chip 50Ω termination resistors. The inputs
can be configured for CML or other high-speed logic. An
input data-retiming latch can be enabled to reject input
pattern-dependent jitter when a clock signal is available.
The MAX3865 provides laser bias current and modulation
current monitors, as well as a failure detector, to indicate
the laser operating status. These features are all imple-
mented on an 81mil ✕ 103mil die; the MAX3865 is also
available as a 32-pin QFN package.
ꢀ Selectable Data Retiming Latch
ꢀ Bias and Modulation Current Monitors
ꢀ Failure Detector
ꢀ ESD Protection
Ordering Information
PART
MAX3865EGJ
MAX3865E/D
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
32 QFN
Applications
SONET/SDH Transmission Systems
Dice*
Add/Drop Multiplexers
*Dice are designed to operate from -40°C to +85°C , but are tested
and guaranteed at T = +25°C only. Contact factory for availability.
Digital Cross-Connects
A
Section Regenerators
Pin Configuration appears at end of data sheet.
2.5Gbps Optical Transmitters
Typical Applications Circuit
+3.3V
+3.3V
LED
+3.3V
200Ω
200Ω
20Ω
LASER
L
P
L
P
0.056µF
MODN
20Ω
20Ω
50Ω
50Ω
DATA-
DATA+
DATA-
DATA+
15Ω
0.056µF
MODQ
V
V
DR
+3.3V
MAX3865
MAX3892
2.5Gbps SERIALIZER
CLK+
BIAS
BIAS_X
CR
50Ω
50Ω
CLK+
MD
MD_X
CLK-
CLK-
REPRESENTS A CONTROLLED-IMPEDANCE
TRANSMISSION LINE
R
R
R
R
AMCSET
MODMAX
BIASMAX
APCSET
†
Covered by U.S. Patent numbers 5,883,910, 5,850,409, and other patent pending.
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
2.5Gbps Laser Driver with Automatic
Modulation Control
ABSOLUTE MAXIMUM RATINGS
Voltage at Any Pin...............................................................+7.0V
Current into BIAS Pin ......................................-20mA to +150mA
Supply Voltage (V ) ............................................-0.5V to +7.0V
Current into MODQ and MODN Pins ..............-20mA to +100mA
Current into MD Pin...........................................-10mA to +10mA
Operating Junction Temperature .....................-55°C to +150°C
Storage Temperature Range.............................-55°C to +150°C
CC
Voltage at V , V , DATA+, DATA-,
CR DR
CLOCK+, and CLOCK- Pins ..................-0.5V to (V
Voltage at DATA+ and
+ 0.5V)
CC
DATA- Pins ..................................(V - 1.2V) to (V + 1.2V)
Continuous Power Dissipation (T = +85°C)
DR
DR
A
Voltage at CLK+ and CLK- Pins......(V - 1.2V) to (V + 1.2V)
32-Pin QFN (derate 21.2mW/°C above +85°C) ................1.3W
Lead Temperature (soldering, 10s) .................................+300°C
Processing Temperature (die) .........................................+400°C
CR
CR
CC
Voltage at MODQ and MODN Pins ................0V to (V
+ 1.5V)
Voltage at Any Other Pins (RTEN, EN0, EN1, FAIL,
MODMAX, BIASMAX, AMCSET, APCSET, MD_X, BIAS,
BIAS_X, BIASMON, MODMON) ............-0.5V to (V + 0.5V)
CC
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
= +3.14V to +3.6V or +4.5V to +5.5V, T = -40°C to +85°C. Typical values are at V
= +3.3V, I
= 50mA, I
MOD
= 30mA,
UNITS
mA
CC
A
CC
BIAS
T
= +25°C, unless otherwise noted.) (Notes 1, 2, 3)
A
PARAMETER
SYMBOL
CONDITIONS
= +3.14V to +3.6V (Note 4)
= +4.5V to +5.5V,
MIN
TYP
MAX
V
V
68
85
CC
CC
Power-Supply Current
I
CC
69
90
typical current at V
= +5.0V (Note 4)
CC
Differential Input Voltage
V
Data and clock inputs (Figure 2)
0.2
1.3
40
1.6
CC
0.4V
Vp-p
V
ID
V
+
Instantaneous Input Voltage
Single-Ended Input Resistance
Data and clock inputs (Figure 2) (Note 5)
Input to V , V
50
20
17
60
DR CR
f
2.7GHz
Input Return Loss, for Data+,
Data-, Clock+, and Clock-
RL
dB
IN
2.7GHz < f < 4GHz
Bias-Current Setting Range
Bias Off Current
1
100
0.1
15
mA
mA
%
EN0, EN1 = low
APC off
I
I
= 100mA
= 1mA
BIAS
BIAS
Bias-Current Setting Accuracy
0.1
48
mA
Compliance Voltage for BIAS
and BIAS_X
V
+
CC
(Note 5)
1
5
V
0.4
I
to I
Ratio
BIASMON
mA/mA
mA
BIAS
Modulation-Current Setting
Range
I
60
MOD
Modulation Off Current
EN0, EN1 = low
AMC off
0.1
15
mA
%
I
I
= 60mA
= 5mA
MOD
MOD
Modulation-Current Setting
Accuracy
0.25
mA
V
V
+
CC
1.2
5.5
+3.14V
+4.5V
V
+3.6V
+5.5V
1.8
1.8
Compliance Voltage for MODQ
and MODN
CC
(Note 5)
(Note 5)
V
V
CC
I
to I
Ratio
MODMON
32
mA/mA
MOD
Compliance Voltage for
BIASMON and MODMON
+
CC
0.4
1.8
V
V
Voltage at MD Pin
V
1.0
MD
2
_______________________________________________________________________________________
2.5Gbps Laser Driver with Automatic
Modulation Control
ELECTRICAL CHARACTERISTICS (continued)
(V
= +3.14V to +3.6V or +4.5V to +5.5V, T = -40°C to +85°C. Typical values are at V
= +3.3V, I
= 50mA, I = 30mA,
MOD
CC
A
CC
BIAS
T
A
= +25°C, unless otherwise noted.) (Notes 1, 2, 3)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
%
I
I
= 1mA
= 36µA
15
10
15
10
MD
MD
Bias-Setting Accuracy at
MD Pin
µA
%
I
I
= 1mA
= 36µA
MD
Modulation-Setting
Accuracy at MD Pin
(Note 6)
µA
V
MD
EN0, EN1, and RTEN Input High
EN0, EN1, and RTEN Input Low
FAIL Output High
2.0
2.4
0.8
V
Source 50µA
Sink 100µA
V
FAIL Output Low
0.4
5.0
V
FAIL Current
Low state, V forced to V
OL
mA
ps
ps
%
CC
Setup/Hold Time
t
, t
SU HD
(Figure 2) (Note 5)
100
80
Output Edge Speed
Output Overshoot
Enable/Startup
t , t
R
Load = 20 , 20% to 80% (Notes 5, 7)
(Notes 5, 7)
84
130
F
9
APC and AMC off
(Notes 2, 5)
150
ns
Maximum CID
bit
psp-p
Deterministic Jitter
Random Jitter
(Notes 2, 5)
22
1.6
1
50
(Notes 5, 7)
ps
RMS
AMC Pilot Tone Frequency
f
MHz
AMC
Note 1: AC characterization performed using the circuit in Figure 1.
Note 2: Measured using a 2.5Gbps 213 - 1 PRBS with 80 0’s and 80 1’s input data pattern.
Note 3: Specifications at -40°C are guaranteed by design and characterization.
Note 4: V
current excludes the current into MODQ, MODN, BIAS, BIAS_X, MODMON, and BIASMON pins.
CC
Note 5: Guaranteed by design and characterization.
Note 6: Measured with low-frequency data. Instantaneous current into MD pin range is 36µA to 1000µA.
Note 7: Measured using a 2.5Gbps repeating 0000 0000 1111 1111 pattern.
_______________________________________________________________________________________
3
2.5Gbps Laser Driver with Automatic
Modulation Control
V
CC
V
CC
RTEN
DATA-
V
CC
33Ω
33Ω
50Ω
50Ω
OSCILLOSCOPE
DATA-
0.1µF
MODN
MODQ
DATA+
PATTERN GENERATOR
CLK+-
DATA+
50Ω
V
V
DR
CC
0.1µF
50Ω
V
CR
50Ω
50Ω
CLK+
CLK-
MAX3865
V
BIAS
CC
CLK-
BIAS_X
V
CC
GND EN1 EN0
Figure 1. Test Circuit
V
+ 0.4V
CC
CLK+
CLK-
0.1V–0.8V
1.3V
V
CC
+ 0.4V
t
t
HD
SU
DATA+
DATA-
0.1V–0.8V
1.3V
(DATA+) - (DATA-)
V
= 0.2Vp-p–1.6Vp-p
ID
I
MODQ
5mA–60mA
Figure 2. Required Input Signal, Setup/Hold-Time Definition, and Output Polarity
_______________________________________________________________________________________
4
2.5Gbps Laser Driver with Automatic
Modulation Control
Typical Operating Characteristics
(T = +25°C, unless otherwise noted.)
A
OPTICAL EYE DIAGRAM
(EXTINCTION RATIO = 8.25dB,
-1 PRBS AT 2.5Gbps, 1.87GHz FILTER)
ELECTRICAL EYE DIAGRAM
ELECTRICAL EYE DIAGRAM
13
(I
= 60mA)
(I
= 30mA)
2
MODQ
MODQ
13
13
PATTERN 2 - 1 PRBS
DATA RATE = 2.5Gbps
PATTERN 2 - 1 PRBS
DATA RATE = 2.5Gbps
58ps/div
58ps/div
58ps/div
SUPPLY CURRENT (I ) vs. TEMPERATURE
CC
(EXCLUDES BIAS AND MODULATION CURRENTS)
DETERMINISTIC JITTER
TYPICAL DISTRIBUTION OF RISE TIME
(WORST-CASE CONDITIONS)
vs. TEMPERATURE (I
= 60mA)
MODQ
80
100
90
80
70
60
50
40
30
20
10
0
30
25
20
15
10
5
ELECTRICAL
MEASUREMENT
75
I
= 60mA
MODQ
V
= +3.14V
CC
V
= +5.0V
T
= +85°C
CC
A
70
65
60
55
50
V
= +3.3V
CC
0
-40
-15
10
35
60
85
-40
-20
0
20
40
60
80
100 102 104 106 108 110 112 114 116 118 120
RISE TIME (ps)
TEMPERATURE (°C)
TEMPERATURE (°C)
TYPICAL DISTRIBUTION OF FALL TIME
(WORST-CASE CONDITIONS)
DIFFERENTIAL |S11| vs. FREQUENCY
-15
30
25
20
15
10
5
ELECTRICAL
MEASUREMENT
-17
-19
-21
-23
-25
-27
-29
-31
-33
-35
I
= 60mA
MODQ
V
= +3.14V
CC
T
= +85°C
A
0
100 102 104 106 108 110 112 114 116 118 120
FALL TIME (ps)
0
500 1000 1500 2000 2500 3000 3500 4000
FREQUENCY (MHz)
_______________________________________________________________________________________
5
2.5Gbps Laser Driver with Automatic
Modulation Control
Pin Description
PIN
NAME
FUNCTION
1, 8, 19,
22, 28
V
Positive Supply Voltage
CC
2
3
4
5
6
7
DATA-
Complementary Data Input, with On-Chip Termination
Data Input, with On-Chip Termination
DATA+
V
V
Termination Reference Voltage for Data Inputs
DR
CR
Termination Reference Voltage for Clock Inputs
CLK+
CLK-
Clock Input for Data Retiming, with On-Chip Termination
Complementary Clock Input for Data Retiming, with On-Chip Termination
9, 16, 23,
24, 25
GND
No Internal Connection. Tie to ground.
10
11
12
13
14
15
17
18
20
21
26
RTEN
EN0
Data Retiming Enable Input, TTL Compatible, Active-High
Operating Mode Input, TTL Compatible
EN1
Operating Mode Input, TTL Compatible
FAIL
Fault Warning, TTL Compatible. Low for fault condition.
BIASMON
MODMON
BIAS_X
BIAS
Bias-Current Monitor. Open-collector type, tie to V if not used.
CC
Modulation-Current Monitor. Open-collector type, tie to V if not used.
CC
Bias Shunt. Always tie to the BIAS pin.
Laser Bias-Current Output. Connect to the laser via an inductor.
Modulation-Current Output to Dummy Load
Modulation-Current Output to Laser
MODN
MODQ
MD
Feedback Input from Monitor Diode
Monitor Diode Shunt. Connect to GND when laser diode to monitor current gain ≤ 0.005. Connect to
the MD pin for gain ≥ 0.02. For 0.005 < gain < 0.02 connect to either GND or the MD pin.
27
MD_X
29
30
AMCSET
APCSET
Monitor Diode Modulation-Current (Peak-to-Peak) Set Point
Monitor Diode Bias-Current (Average) Set Point
Connect an external resistor to ground to program I
in the MANUAL and APC modes. The
MOD
resistor sets the maximum I
but cannot add to it.
in AMC mode. The AMC loop may reduce I
from its maximum
31
MODMAX
BIASMAX
MOD
MOD
Connect an external resistor to ground to program I
in the MANUAL mode. The resistor sets the
BIAS
32
EP
maximum I
in the APC and AMC modes. The APC loop may reduce I
from its maximum but
BIAS
BIAS
cannot add to it.
Exposed
Paddle
The exposed paddle and corner pins must be soldered to ground.
6
_______________________________________________________________________________________
2.5Gbps Laser Driver with Automatic
Modulation Control
Table 1. Mode Selection
EN0
EN1
OPERATING MODE
Shutdown
Manual
DESCRIPTION
Bias and modulation currents off
0
0
1
1
0
1
0
1
BIASMAX programs laser bias, MODMAX programs modulation
APCSET programs laser bias, MODMAX programs modulation
AMCSET programs modulation current and APCSET programs bias
APC
AMC
Operating Mode
The MAX3865 can be set in four operating modes,
depending on applications requirements. Mode selec-
tion is by two TTL-compatible inputs (see Table 1).
Detailed Description
The MAX3865 laser driver consists of two main parts: a
high-speed modulation driver and biasing block as
shown in Figure 4. Outputs to the laser diode are a
switched modulation current and a steady bias current.
Two servo loops may be enabled to control bias and
modulation currents for constant optical power and
extinction ratio.
APC Loop
In APC mode, a servo loop maintains the average
current from the monitor diode at a level set by the
APCSET input. Laser bias current is varied in this mode
to maintain the monitor diode current. The BIASMAX
input must be set to a value larger than the maximum
expected bias current. In this mode, BIASMAX limits the
maximum bias current to the laser if the control loop
The MAX3865 requires a laser with a built-in monitor
diode to provide feedback about the optical output.
The average laser power, as sensed by the monitor
diode, is controlled by the APC servo loop. Peak-to-
peak modulation current is controlled by the AMC servo
loop. The modulation output stage uses a programma-
ble current source with a maximum current of 60mA. A
high-speed differential pair switches this source to the
laser diode. The clock and data inputs to the modula-
tion driver may use CML, PECL, and other logic levels.
The optional clock signal can be used to synchronize
data transitions for minimum pattern-dependent jitter.
fails. The FAIL pin will go low if average I
≠ I
.
MD
APCSET
Mark-Density Compensation
Average power control assumes 50% mark density for
times greater than about 100ns. For long patterns or sit-
uations where 50% mark density does not apply, the
MAX3865 provides mark-density compensation. The
APCSET reference is increased by an amount propor-
tional to the mark density multiplied by the modulation
amplitude. The AMCSET input is used as an estimate of
the peak-to-peak modulation current when the mark
density is not 50%. Mark-density compensation is
active in both APC and AMC control modes.
Clock/Data Input Logic Levels
The MAX3865 is directly compatible with V -refer-
CC
enced CML. Other logic interfaces are possible. For
V
V
-referenced CML or AC-coupled logic, tie V
and
CC
CR
float V
DR
to V . For other DC-coupled differential signals,
CC
and V
AMC Loop
In AMC mode, a servo loop maintains the peak-to-peak
current from the monitor diode at a level set by the
AMCSET input. Laser modulation current is varied in
this mode to maintain the monitor diode current. The
MODMAX input must be set to a value larger than the
maximum expected modulation current. In this mode,
MODMAX limits the maximum modulation current to the
laser if the control loop fails. The FAIL pin will go low if
(Figure 5). To prevent excess power
CR
dissipation in the input matching resistors, keep the
DR
instantaneous input voltage within 1.2V of V
as specified in the electrical characteristics.
or V
CR
DR
Optional Input Data Retiming
To eliminate pattern-dependent jitter in the input data, a
synchronous differential clock signal should be con-
nected to the CLK+ and CLK- inputs, and the RTEN
control input should be tied high. Input data retiming
occurs on the rising edge of CLK+. If RTEN is tied low,
the retiming function is disabled and the input data is
directly connected to the output stage. When no clock
peak-to-peak I
when in the AMC mode. In AMC mode, mark-density
compensation is automatic.
≠ I
. The APC loop is active
AMCSET
MD
is available, tie CLK+ to V , ground CLK- through a
CC
1.5kΩ resistor, and leave V open.
CR
_______________________________________________________________________________________
7
2.5Gbps Laser Driver with Automatic
Modulation Control
Warning Outputs
Table 2. Optical Power Relations
A TTL-compatible, active-low warning flag, FAIL, is set
PARAMETER
Average Power
Extinction Ratio
SYMBOL
RELATION
= (P + P )/2
when:
P
P
r
AVG
AVG
0
1
• One or more of the programmable currents is set at
greater than 150% of the rated maximum for the
chip. A shorted programming resistor would cause
this warning. In this case, the bias and modulation
outputs are shut down to protect the laser.
r
= P / P
1 0
e
e
Optical Power of a
“1”
P
P
P = 2P
✕ r /( r + 1)
e e
1
0
1
AVG
Optical Power of a
“0”
P = 2P
/( r + 1)
e
0
AVG
• Average I
≠ I
in the APC or AMC mode. This
could be caused by too low a setting for maximum
or by a laser that has exceeded its useful life.
MD
APCSET
Optical Amplitude
Pp-p
Pp-p = P - P
1
0
I
BIAS
Laser Slope
Efficiency
• Peak-to-peak I
≠ I
in the AMC mode. This
η
η = Pp-p/I
MOD
MD
AMCSET
could be caused by too low a setting for I
or
MODMAX
Laser to Monitor
Diode Transfer
by a laser which has exceeded its useful life.
ρ
ρ
= I / P
MD AVG
MON
MON
The FAIL flag also is set for a few microseconds follow-
ing power-up, until the servo loops settle. The BIASMON
and MODMON pins can be used to monitor the laser
current and predict the end of the useful laser life before
a failure occurs.
Note: Assuming a 50% average input duty cycle and mark density.
modulation current. These relationships are valid if the
mark density and duty cycle of the optical waveform
are 50%.
Design Procedure
For a desired laser average optical power, P
, and
AVG
optical extinction ratio, r , the required modulation cur-
When designing a laser transmitter, the optical output is
usually expressed in terms of average power and
extinction ratio. Table 2 gives relationships that are
helpful in converting between the optical power and the
e
rent can be calculated based on the laser slope effi-
ciency, η, using the equations in Table 2.
+5V
+5V
20Ω
MODN
MODQ
20Ω
20Ω
DATA-
I
I
MODQ
15Ω
DATA+
BIAS
MAX3865
BIAS
BIAS_X
CLK+
CLK-
I
MD
MD
R
R
R
R
AMCSET
MODMAX
BIASMAX
APCSET
Figure 3. DC-Coupled Laser Circuit
_______________________________________________________________________________________
8
2.5Gbps Laser Driver with Automatic
Modulation Control
formed by the LC circuit must be low enough to limit
the droop.
Laser Current Requirements
Bias and modulation current requirements can be
determined from the laser threshold current and slope
efficiency. The modulation and bias currents under a
single operating condition are:
Number_CID
Droop =
Data_Rate× L ×C
P
P
r −1
If droop = 6.7%, number_CID = 100 and data_rate =
AVG
η
e
I
= 2×
×
MOD
2.5Gbps, then possible values for L and C may be
P
r +1
e
L
= 6µH and C = 0.056µF. Both L and C must be
P
increased in value to reduce droop without ringing.
• For DC-coupled laser diodes:
> I
I
BIAS
TH
Programming the Maximum Bias Current
where I is the laser threshold current.
TH
In AMC (or APC) mode, the bias current needs a limit if
the loop becomes open. R
sets the maximum
BIASMAX
• For AC-coupled laser diodes:
allowed bias current. The bias current is proportional to
the current through R . An internal current regu-
I
MOD
BIASMAX
I
>I
+
BIAS TH
2
lator maintains the band-gap voltage of 1.2V across the
programming resistors. Select the maximum I
gramming resistor as follows:
pro-
BIAS
Given the desired parameters for operation of the laser
diode, the programming of the MAX3865 is explained
in the following text.
1.2V
I
= 480×
BIASMAX
Current Limits
To keep the modulation current in compliance with the
programmed value, the following constraint on the total
modulation current must be made:
R
+2kΩ
BIASMAX
Alternatively, a current DAC forcing I
from the
DAC
BIASMAX pin may set the current maximum:
DC-Coupled Laser Diodes:
I
= 480 ✕ I
BIASMAX
DAC
V
- V
- I
✕ (R + R ) - I ✕ R ≥ 1.8V
BIAS L
CC
DIODE MOD
D
L
When the AMC or APC loop is enabled, the actual bias
current is reduced below the maximum value to main-
tain a constant average current from the monitor diode.
With closed-loop control, the bias current will be deter-
mined by the transfer function of the monitor diode to
laser-diode current. For example, if the transfer function
• For V
—Laser diode bias point voltage
DIODE
(1.2V typ)
RL—Laser diode bias-point resistance (5Ω typ)
RD—Series matching resistor (15Ω typ)
AC-Coupled Laser Diodes:
to the monitor diode is 10.0µA/mA, then setting I
for
MD
500µA will result in I
equal to 50mA.
BIAS
To allow larger modulation current, the laser can be
AC-coupled to the MAX3865 as shown in the Typical
Application Circuit. In this configuration, a constant cur-
rent is supplied from the inductor L . The requirement
P
for compliance in the AC-coupled circuit is as follows:
In manual mode, the bias current I
is I
BIASMAX
as
BIAS
set by R
.
BIASMAX
Programming the Average Monitor
Diode-Current Set Point
The APCSET pin controls the set point for the average
monitor diode current when in AMC or APC mode. The
APCSET current is externally established in the same
manner as the BIASMAX pin. The average monitor
I
MOD
V
−
× R +R ≥1.8V
D L
(
)
CC
2
The AC-coupling capacitor and bias inductor form a
second-order high-pass circuit. Pattern-dependent jitter
results from the low-frequency cutoff of this high-pass
circuit. To prevent ringing:
diode current I
as follows:
can be programmed with a resistor
MD
1.2V
+2kΩ
APCSET
average_I
= 5×
L
P
C
MD
R
+R ≥ 2×
(
)
R
D
L
Alternatively, a current DAC at the APCSET pin can set
the monitor diode current by:
For deviation from 50% duty cycle or for runs of con-
secutive identical digits (CID), the low-frequency corner
average I
= 5 ✕ I
DAC
MD
_______________________________________________________________________________________
9
2.5Gbps Laser Driver with Automatic
Modulation Control
Mark-Density Compensation
Table 3. Connection of the MD_X Pin
in APC Mode
When mark density is expected to deviate from 50% for
periods exceeding 5% of the APC time constant, the
AMCSET pin should be programmed to compensate
the APC set point. The time constant is determined by
the laser to monitor diode gain.
LASER-TO-MONITOR
DIODE-CURRENT GAIN
MD_X SHUNT
CONNECTION
<0.005
0.005 to 0.02
>0.02
GND or Open
(Open or GND) or MD
MD
1.5ns
τ
=
APC
Programming the Peak-to-Peak Monitor
Diode-Current Set Point
G
MD
The AMCSET pin controls the set point for the peak-to-
peak monitor diode current in AMC mode. The peak-to-
peak value of the monitor diode current can be
programmed with a resistor as follows:
∆I
∆I
MONITOR
G
=
MD
LASER
(For example, τ
Set the estimated peak-to-peak monitor diode current
by the following equation:
= 150ns for G
= 0.01mA/mA.)
APC
MD
1.2V
I
= 5×
MD(p−p)
R
+2kΩ
AMCSET
Alternatively a current DAC at the AMCSET pin can set the
monitor diode current by:
1.2V
Estimated I
= 5×
MD(p−p)
R
+2kΩ
AMCSET
I
= 5 ✕ I
DAC
MD(p-p)
Alternatively, a current DAC at the AMCSET pin can set
the monitor diode current by:
Laser Gain Compensation
The MAX3865 may be used in closed-loop operation
with a wide variety of laser-to-monitor diode gains.
Table 3 shows the connection of the MD_X pin for dif-
ferent current-gain ranges.
Estimated I
= 5 ✕ I
DAC
MD(p-p)
Programming the Maximum
Modulation Current
In AMC mode, the modulation current needs a limit if
Current Monitor Outputs
The MAX3865 provides bias and modulation current
monitors. The BIASMON output sinks a current propor-
tional to the bias current:
the loop becomes open. R
sets the maximum
MODMAX
allowed modulation current. The modulation current is
proportional to the current through R
. Select
MODMAX
the maximum I
programming resistor as follows:
MOD
I
BIAS
48
I
=
BIASMON
1.2V
I
= 320×
MODMAX
R
+2kΩ
MODMAX
The MODMON pin sinks a current proportional to the
laser modulation current:
Alternatively, a current DAC forcing I
from the
DAC
MODMAX pin may set the current maximum
I
MOD
32
I
= 320 ✕ I
I
=
MODMAX
DAC
MODMON
When the AMC loop is enabled, the actual modulation
current is reduced from the maximum value to maintain
constant peak-to-peak current from the monitor diode.
With closed-loop control, the modulation current will be
determined by the transfer function of the monitor diode
to laser diode current. For example, if the transfer func-
The BIASMON and MODMON pins should not be
allowed to drop below 1.8V. They should be tied to V
when not in use.
CC
tion to the monitor diode is 10.0µA/mA, then setting I
MD
for 500µA will result in I
equal to 50mA.
MOD
In manual mode, the modulation current I
MODMAX
is set by
MOD
R
.
10 ______________________________________________________________________________________
2.5Gbps Laser Driver with Automatic
Modulation Control
V
CC
RTEN
20Ω
MODN
MODQ
o
1
I
MODO
MUX
D
DATA
CLK
Q
C
R
D
D
I
BIAS
BIAS
MD
MONITOR DIODE
FEEDBACK
I
MD
CONTROL LOGIC
SHUTDOWN
-
MODULATION
CONTROL
∑
+
-
EN0
EN1
LOOP
MONITOR
∑
BIAS
CONTROL
+
OVERCURRENT
x5
x5
x320
x480
FAIL
MAX3865
V
V
V
V
BG
BG
BG
BG
R
R
R
R
BIASMAX
AMCSET
APCSET
MODMAX
Figure 4. Functional Diagram
V
CC
V
MODQ
MODN
GND
CC
V
DR
50Ω
50Ω
DATA+
DATA-
I
MOD
DATA AND CLOCK INPUT CIRCUITS ARE EQUIVALENT
GND
GND
Figure 6. Equivalent Modulation Output Circuit
Figure 5. Equivalent Input Circuit
______________________________________________________________________________________ 11
2.5Gbps Laser Driver with Automatic
Modulation Control
recognizing that Maxim products are not designed or
Applications Information
authorized for use as components in systems intended
for surgical implant into the body, for applications
intended to support or sustain life, or for any other appli-
cation where the failure of a Maxim product could create
a situation where personal injury or death may occur.
Layout Considerations
To minimize loss and crosstalk, keep the connections
between the MAX3865 output and the laser diode as
short as possible. Use good high-frequency layout
techniques and multilayer boards with uninterrupted
ground plane to minimize EMI and crosstalk. Circuit
boards should be made using low-loss dielectrics. Use
controlled-impedance lines for the clock and data
inputs as well as the modulation output.
Chip Information
TRANSISTOR COUNT: 1690
Substrate Connected To GND
PROCESS: Bipolar
References
For further information, refer to the application notes for
fiber optic circuits, HFAN-02, on the Maxim web page.
DIE SIZE: 81mil ✕ 103mil
Laser Safety and IEC 825
Using the MAX3865 laser driver alone does not ensure
that a transmitter design is compliant with IEC 825. The
entire transmitter circuit and component selections must
be considered. Each customer must determine the
level of fault tolerance required by their application,
Pin Configuration
TOP VIEW
V
1
2
3
4
5
6
7
8
24 GND
23 GND
CC
DATA-
DATA+
22
V
CC
V
V
21 MODQ
20 MODN
DR
MAX3865
CR
CLK+
CLK-
19
V
CC
18 BIAS
V
17 BIAS_X
CC
THE EXPOSED PADDLE MUST BE SOLDERED TO
SUPPLY GROUND ON THE CIRCUIT BOARD
12 ______________________________________________________________________________________
2.5Gbps Laser Driver with Automatic
Modulation Control
Chip Topography
BP21
N.C.
N.C.
V
BP8
BP7
BP6
BP5
CC
BP22
BP23
DATA-
DATA+
V
CC
BP24
MODQ
MODN
V
DR
CR
81mil
2.06mm
BP25
BP26
V
BP4
BP3
V
CC
CLK+
CLK-
BP27
BP28
BIAS
BP2
BP1
BIAS_X
V
CC
103mil
2.62mm
Note: N.C. means no external connection permitted. Leave these pads unconnected.
______________________________________________________________________________________ 13
2.5Gbps Laser Driver with Automatic
Modulation Control
Pad Coordinates
NAME
PAD
BP1
COORDINATES (µm)
46, 46
NAME
N.C.
N.C.
PAD
BP21
COORDINATES (µm)
2382, 1423
V
CC
CLK-
BP2
46, 241
BP22
BP23
BP24
BP25
BP26
BP27
BP28
BP29
BP30
BP31
BP32
BP33
BP34
BP35
BP36
BP37
BP38
BP39
BP40
2382, 1229
2382, 1034
2382, 840
2382, 646
2382, 451
2382, 257
2382, 62
CLK+
BP3
46, 435
V
CC
V
V
BP4
46, 629
MODQ
MODN
CR
DR
BP5
46, 824
DATA+
DATA-
BP6
46, 1018
V
CC
BP7
46, 1213
BIAS
V
BP8
46, 1407
BIAS_X
GND
CC
N.C.
BP9
151, 1607
346, 1607
540, 1607
735, 1607
929, 1607
1123, 1607
1318, 1609
1512, 1609
1707, 1607
1901, 1607
2095, 1607
2290, 1607
2287, -153
2093, -153
1898, -153
1704, -153
1510, -153
1315, -153
1121, -153
926, -153
732, -153
538, -153
343, -153
149, -153
GND
BP10
BP11
BP12
BP13
BP14
BP15
BP16
BP17
BP18
BP19
BP20
GND
BIASMAX
MODMAX
APCSET
AMCSET
MODMON
BIASMON
FAIL
GND
V
GND
CC
MD_X
MD
EN1
EN0
GND
N.C.
N.C.
RTEN
GND
GND
Coordinates are for the center of the pad.
Coordinate 0, 0 is the lower left corner of the passivation opening for pad 1.
14 ______________________________________________________________________________________
2.5Gbps Laser Driver with Automatic
Modulation Control
Package Information
______________________________________________________________________________________ 15
2.5Gbps Laser Driver with Automatic
Modulation Control
Package Information (continued)
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
相关型号：
MAX38650
Tiny 1.8V to 5.5V Input, 390nA IQ, 100mA nanoPower Buck Converter with 100% Duty Cycle Operation
MAXIM
MAX38650AANT+
Tiny 1.8V to 5.5V Input, 390nA IQ, 100mA nanoPower Buck Converter with 100% Duty Cycle Operation
MAXIM
MAX38650BANT+
Tiny 1.8V to 5.5V Input, 390nA IQ, 100mA nanoPower Buck Converter with 100% Duty Cycle Operation
MAXIM
©2020 ICPDF网 联系我们和版权申明