QThe ADN2871 laser driver datasheet gives a recommended differential drive
circuit for driving a VCSEL Laser diode. The recommended impedance of the
transmission lines between the driver and laser diode are 20ohm. How critical
is it that these lines are matched to 20ohms. The closest we can get to is
about 30ohm. The data
rates which we are going use is 100Mbps and 1Gbps.
AI would recommend ADN2873 instead. When the selected TOSA turn on resistance is
only about 15ohm or 10ohm,
the transmission line impedance of about 25 ohm to 30ohm is preferred.
Our solution needs the proper termination at the LDD side. So, a termination
resistor close/matched to the transmission line impedance is preferred. In this
passive termination circuit, the IMOD current high frequency components will be
divided per the termination resistance vs. the laser diode turn on resistance.