Temperature compensation in optical sensing system

Disclosed is a temperature compensation circuit for a light source (e.g., light emitting diode (LED)) whose radiant energy output decreases when ambient temperature increases. The circuit includes first means for sourcing a first current that increases proportional to an increase in ambient temperature, and second means for sourcing a second current that is first order independent of ambient temperature. The circuit further includes a weighted current adder for sourcing a third current by combining the first and second currents with first and second weights applied to the first and second currents respectively. The circuit further includes third means responsive to the third current for supplying a fourth current to the light source to maintain a radiant energy output of the light source constant independent of ambient temperature.