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| 型号： | ADN2873ACPZ-RL |
| 厂商： | Analog Devices Inc |
| 文件页数： | 13/20页 |
| 文件大小： | 0K |
| 描述： | IC LASER DRIVER 4.25GBPS 24LFCSP |
| 标准包装： | 5,000 |
| 类型： | 激光二极管驱动器（光纤） |
| 数据速率： | 4.25Gbps |
| 通道数： | 1 |
| 电源电压： | 3 V ~ 3.6 V |
| 电流 - 电源： | 31mA |
| 电流 - 调制： | 90mA |
| 电流 - 偏置： | 100mA |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 24-VFQFN 裸露焊盘，CSP |
| 供应商设备封装： | 24-LFCSP-VQ（4x4） |
| 包装： | 带卷 (TR) |
| 安装类型： | 表面贴装 |
ADN2873
THEORY OF OPERATION
Laser diodes have a current-in to light-out transfer function, as
shown in Figure 28. Two key characteristics of this transfer
function are the threshold current, I TH , and the laser slope in the
linear region beyond the threshold current, referred to as the
slope efficiency, LI.
CONTROL METHODS
The ADN2873 has two methods for setting the average power
(P AV ) and ER. The laser optical output average power and
extinction ratio are configurable by using the voltage setting or
the resistor setting. In voltage setting mode, a microcontroller
P1
ER =
P AV =
P1
P O
P1 + P O
2
DAC can drive the PAVREF and ERREF pins with programmable
voltages. Alternatively, in resistor setting mode, the resistor
divider or potentiometers can set proper voltages at the PAVSET
and ERSET pins. Refer to Figure 29 and Figure 30 for details.
P AV
Δ P
VOLTAGE SETPOINT CALIBRATION
P O
Δ I
LI =
Δ P
Δ I
The ADN2873 allows interface to a microcontroller for both
control and monitoring (see Figure 29). The average power and
extinction ratio can be set using the microcontroller DACs to
I TH
CURRENT
provide controlled reference voltages, PAVREF and ERREF.
Figure 28. Laser Transfer Function
PAVREF = P AV × R SP × R PAV
(V)
LASER CONTROL
Typically, laser threshold current and slope efficiency are both
ERREF =
I MOD × R ERSET
100
(V)
functions of temperature. For FP-type and/or DFB-type lasers,
the threshold current increases and the slope efficiency decreases
with increasing temperature. In addition, these parameters vary
as the laser ages. To maintain a constant optical average power
and a constant optical extinction ratio over temperature and
laser lifetime, it is necessary to vary the applied electrical bias
current and modulation current to compensate for the changing
LI characteristics of the laser.
Average Power Control Loop (APCL)
The APCL compensates for changes in I TH and LI by varying
IBIAS. Average power control is performed by measuring the
monitor photodiode (MPD) current, IMPD. This current is
bandwidth limited by the MPD. This is not a problem because
the APCL is required to respond to the average current from the
MPD.
Extinction Ratio (ER) Control
where:
P AV is the laser optical average power output required.
R SP is the optical responsivity (in amperes per watt).
R PAV = R ERSET = 1 kΩ.
I MOD is the modulation current.
In voltage setpoint mode, R PAV and R ERSET must be 1 kΩ resistors
with a 1% tolerance and a temperature coefficient of 50 ppm/°C.
Power-On Sequence in Voltage Setpoint Mode
During power-up, an initial sequence allows 25 ms before
enabling the alarms. Therefore, the user must ensure that the
voltages applied to PAVREF and ERREF are stabilized within
20 ms after ramp-up of the power supply. If supplying the
PAVREF and ERREF voltages after the 25 ms, the alarms and
FAIL circuitry kick in before the voltages are stabilized to
PAVREF and ERREF, which causes an unexpected failure.
ER control is implemented by adjusting the modulation current.
Temperature calibration is required to adjust the modulation
current to compensate for variations of the laser characteristics
with temperature.
Rev. 0 | Page 13 of 20
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