M02094-12 Datasheet, PDF (30/46 Pages) M/A-COM Technology Solutions, Inc. – EPON FTTH modules

M02094-12
3.3 or 5 Volt VCSEL/FP Laser Driver IC for Applications to 2 Gbps
Rev V5
3.3.7
Modulation Control
There are two programmable control lines for controlling the modulation current and its temperature compensation.
These inputs can be programmed simply with a resistor to ground .
The modulation current amplitude is controlled by the MOD_SET input pin. The modulation current is temperature
compensated by the TC_SLOPE input.
If the temperature compensation at TC_SLOPE is disabled, the modulation output current is simply:
IOUT = 42 x (1.3V / R_MODSET) when CC_SEL is low
and
IOUT = 22 x (1.3V / R_MODSET) when CC_SEL is high and a 50Ω VCSEL is used.
Where R_MODSET is the resistance from pin MOD_SET to ground.
To temperature compensate the modulation current, choose R_TCSLOPE to meet the following relationship:
R_TCSLOPE = 19.5*(TC)^-1.5, where TC is the desired slope of the modulation current from 25°C to 85°C in%/°C and
R_TCSLOPE is in kΩ. If no temperature compensation is desired, leave R_TCSLOPE open.
In any case, R_TCSLOPE will have negligible effect at M02094 case temperatures below 10°C.
For example:
Given a common cathode VCSEL with a desired modulation current at low temperatures of 10mA and a tempera-
ture coefficient of -0.5%/°C at high temperatures (which will require a laser driver temperature coefficient of
+0.5%).
Choose R_MODSET = 22 x (1.3V / 10mA) = 2.8kΩ.
Choose R_TCSLOPE =19.5*(0.5)^-1.5 kΩ = 55kΩ.
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