M02068_17 Datasheet, PDF (9/18 Pages) M/A-COM Technology Solutions, Inc. – 3.3 Volt Laser Driver IC for 155/622 Mbps

Functional Description
3.2
Features
• Rise and fall times <180 ps
• Operates with +3.3 volt supply
• DC or AC-coupled modulation drive
• Independently programmable laser bias (to 100 mA) and modulation currents (to 85 mA)
• Automatic laser power control, with programmable temperature compensation and ‘Slow-Start’
• Bias and modulation current monitors
• Failure monitor
• Available in BCC+24 , TQFP32 and DIE packages
• Available in RoHS compliant packages
3.3
Modulator
The modulator output stage is designed to drive up to 85 mA in either AC-coupled or DC-coupled mode. DC-
coupled performance depends on the laser used.
The CX02068 modulation output is optimized for driving a 25Ω dynamic load; the minimum required voltage at
OUT+ and OUT- is 0.6 V. To interface with the laser diode, a matching resistor (RD) is required for impedance
matching. An RC shunt network is necessary to compensate for the laser diode parasitic inductance, thereby
improving the optical eye. Typical values are R_SHUNT = 51Ω, C_SHUNT = 3.3 pF
Any capacitive loading at the cathode of a laser diode will degrade the optical output performance. An inductor is
used to isolate the BIAS pin from the laser cathode.
Figure 3-2. Typical modulation current vs R_MODSET(3.3V)
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
0
5000
10000 15000 20000 25000 30000 35000
R_MODSET (Ω )
02068-DSH-001-C
Mindspeed Technologies^®
7
Mindspeed Proprietary and Confidential