A laser driver circuit includes a laser APC circuit receiving a monitor
current indicative of the average optical output power of a laser diode
and providing a bias adjust signal for adjusting a bias current for the
laser diode. The laser APC circuit includes a first non-linear impedance
circuit receiving the monitor current and generating a first voltage
using a first non-linear current-to-voltage transfer function, a second
non-linear impedance circuit receiving a reference current and generating
a second voltage and being implemented using the same or a scaled version
of the first non-linear current-to-voltage transfer function, and a
comparator for comparing the first voltage with the second voltage and
providing the bias adjust signal indicative of the difference between the
first and second voltages. The first non-linear current-to-voltage
transfer function has difference resistance portions for increasing the
dynamic range of the current-to-voltage conversion.