US Patent 9325920 Processing of time-of-flight signals

Described herein is a method and sensor of processing time-of-flight (TOF) signals in a TOF camera system including an illumination unit and an imaging sensor. The method comprises illuminating the scene with light at a first frequency, detecting reflected light from at least one object in the scene at the first frequency, and determining a phase measurement using I and Q values. In addition, the scene is illuminated with light at a second frequency, the second frequency being 2−n of the first frequency where n=1, 2, . . . , etc., and the signs of I and Q values for both the first and second frequencies is used to determine the presence of aliasing in the phase measurement so that it can be corrected. The phase measurement is then corrected for aliasing and the effective range of the TOF camera system is extended by multiples of 2n. In addition, relative signal strength needs to be considered in accordance with the reflectivity of objects within the scene. For a reflectivity of 4% and no aliasing, the ability to detect an object decreases with distance (30). For an aliased phase measurement for an object with a reflectivity of 100%, the ability to detect the object is substantially constant (35).