A circuit and method are provided to control the strength of signals from an array of photo-detectors in an optical navigation sensor. In one embodiment, the method includes receiving a current signal from an automatic gain control (AGC) photo-detector and generating an AGC signal in response thereto; generating an illumination control signal in response to the AGC signal; and coupling the illumination control signal to an illuminator configured to illuminate at least a portion of an array of photo-detectors with light reflected from a surface to sense displacement of the optical navigation sensor relative to a surface, and adjusting illumination from the illuminator. Other embodiments are also disclosed.