Smart Pixel Camera
Why are the pixels in the SMARTIEHS camera smart?
The smart-pixel camera is planned to feature 10x10 channels being equipped with a 140x140-pixel CMOS imager each, summing up to a total resolution of about 2 megapixels. Within this project, 5x5 channels are being produced.
The figure above shows the configuration of the detector part of the SMARTIEHS inspection system. The smart-pixel imager ICs are packaged into modules that are placed in a 5x5 matrix at the camera board which transfers the images via a high speed frame grabber to the PC.
The imagers are dedicated to Low-Coherence Interferometry (LCI) and Laser Interferometry (LI). During a LCI measurement the object is moved with constant speed over a distance corresponding to the depth range. The figure below shows the typical optical signal (interferogram) for one detector pixel generated in this process. By detecting the position of the peak of the interferogram envelope for every pixel, the topography of the object can be reconstructed. Usually the imager frame rate limits the depth scan speed and therefore the acquisition time.
To speed up the topography acquisition, a dedicated imager has been developed. The core innovation is the smart-pixel architecture. The optical signal is demodulated at the pixel level. In every pixel an electronic circuit applies I-Q direct demodulation capable of a maximum demodulation frequency of 100 kHz. This corresponds to a frame rate of 400000 frames per second for a conventional image sensor.
The electronic circuit at the pixel level is very versatile and not only allows amplitude demodulation but also the extraction of the modulation phase. Furthermore, conventional grey-level images can be acquired. The architecture is therefore well suited not only for LC and LCI but also for vibrometry.
Smart-pixel module back and front side, equipped with smart-pixel CMOS image sensor