M02061 Datasheet, PDF (34/37 Pages) M/A-COM Technology Solutions, Inc. – 3.3 or 5 Volt Laser Driver

Applications Information
Figure 4-2. Application Diagram, VCC = 5V Laser DC Coupled Example
VCC=5V
VCC3
VCC3
D_IN+
D_IN-
Internal
3.3V reg.
Internal Power Bus
Input
Buffer
D - FF
VCC3 -1.3V
Output
Buffer
Laser
Driver
Input
Buffer
TX
Disable
Safety
Circuitry with
Latched Fault
Modulation
Control
Automatic Power Control
(laser bias current)
V_CC
SPST switch
SV_CC
OUT-
OUT+
GND₀
IBIAS_OUT
IPIN
V CC
(M02061-21
only)
VCC3
(M02061-12
only)
4.2
Video Operation
The M02061 can be used to transmit digital video optical data even in the presence of the pathological signal. This
is done by fully DC coupling the signal from the input to the laser output.In most data communications applications,
AC coupling occurs at 3 points in a laser driver schematic: the data inputs, the APC control, and coupling the
modulation current to the laser. In the M02061 DC coupling can be used at all 3 of these points.The data inputs can
be DC coupled using PECL or CML levels (see Section 3.3.3, “Data Inputs”). LVDS signals can be DC coupled with
level shifting.The APC of the bias current is controlled by feedback from the monitor photo diode in the laser
package in most communications applications. In video applications this monitor photo diode should not be used if
the pathological pattern may occur. Instead, the APC should be controlled in an “open loop” configuration. (Open
loop simply means a monitor photo diode is not used). In the open loop configuration the APC is controlled by a
resistor or a thermistor network or a look-up table. This removes AC time constants from the bias current. In
Figure 4-3 the BIASmon pin is connected to the APCset pin. In this case the bias current is IBIAS = 100 x (1.3V /
RAPCset). The modulation current output OUT+ can be DC coupled to the laser as shown in Figure 4-3. There are
no AC time constants in the modulation current amplitude in this configuration.
02061-DSH-001-G
Mindspeed Technologies^®
34
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