AMCW

AMCW, or Amplitude Modulated Continuous Wave, is a technique used in time-of-flight (ToF) cameras to measure distances to objects in a scene. In AMCW systems, the illumination is modulated by a sinusoidal waveform and the camera analyzes the phase of the reflected light relative to the emitted signal to determine depth. This phase-based approach allows rapid acquisition of depth information, producing 2D depth maps or 3D point clouds.

The core principle relies on the relationship between the phase shift φ and the round-trip distance. If the light is modulated at frequency f, the distance to the target is given by d = (c · φ) / (4πf), where c is the speed of light. Because φ is measured modulo 2π, the unambiguous range is limited for a single frequency, and many AMCW systems use multiple modulation frequencies to resolve distance through phase unwrapping.

AMCW ToF cameras are typically built with an IR light source and a demodulating sensor or dedicated phase detectors. Common hardware options include infrared LEDs or VCSELs and sensors designed for high-frequency demodulation. Multi-frequency approaches improve accuracy and extend range, while inline processing yields depth and confidence information for each pixel.

Applications span consumer depth cameras, robotics, augmented reality, autonomous vehicles, and industrial inspection. Advantages of AMCW include fast frame rates and good performance in moderately challenging lighting; limitations include phase ambiguity, multipath interference, material reflectivity effects, and the need for careful calibration to convert phase data into accurate depth measurements.

See also: time-of-flight imaging, ToF camera, phase-based depth sensing, pulsed ToF.