M02069_17 Datasheet, PDF (34/45 Pages) M/A-COM Technology Solutions, Inc. – 3.3 or 5 Volt VCSEL/FP Laser Driver IC for Applications to 4.3 Gbps

M02069-12
3.3 or 5 Volt VCSEL/FP Laser Driver IC for Applications to 4.3 Gbps
Rev V2
3.3.12
Video Operation
The M02069 can be used to transmit video optical data even in the presence of the pathological pattern. 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 three points in a laser driver schematic: the data
inputs, the APC control, and coupling the modulation current to the laser. In the M02069, DC coupling can be used
at all three of these points. With DC coupling the laser output will not be a function of the data input one/zero den-
sity.
The data inputs can be DC coupled using PECL or CML levels.
The APC of the bias current is controlled by feedback from the monitor photodiode in the laser package in most
communications applications. In video applications this monitor photodiode 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 photodiode is not used). In the open loop configuration the APC is controlled by a resistor or a
thermistor network or a look-up table and DAC. This removes AC time constants from the bias current. In
Figure 3-6 the BIASmon pin is connected to the APCset pin. In this case the bias current is:
IBIAS = 45.7 x (1.35V / RAPC_SET)
The modulation current output OUT+ can be DC coupled to the laser as shown in Figure 3-6. There are no AC
time constants in the modulation current amplitude in this configuration.
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