The use of the external resistor RPhoto provides a flexible means of scaling the VPhoto
dynamic range to fit within the APC reference threshold dynamic range. The dynamic
range of the photo detector current can vary widely over different TOSA types for a
given range of LD bias currents. With appropriate choice of the external RPhoto, a
consistent dynamic range of VPhoto can be achieved over a wide range of photo
detector currents. This allows maximum utilization of the available 8-bit resolution for
APCVRef to define the loop set point.