A sensor element that has a function for modulating, in a time domain, a detection of electrons generated by light in the inside of a pixel, such as “Device and Method for the Detection and Demodulation of an Intensity-modulated Radiation Field (see Patent Document 1)” announced in 1994 or the like, is also referred to as “a lock-in pixel”.
If the sensor element encompassing the foregoing lock-in pixels is applied to a buried photodiode structure used in a recent CMOS image sensor so that a lock-in image sensor can be achieved, a sensor that can be manufactured at a low price and can achieve a high performance is expected to be obtained because CMOS image sensor is superior in mass productivity.
For example, a three-dimensional imaging system that includes a two-dimensional array implemented by light-detection detector-pixels, dedicated electronic circuits and corresponding processing circuits, which are merged on a common IC by using a CMOS manufacturing system, is proposed (see Patent Document 2). In one embodiment of Patent Document 1, each detector has a corresponding high speed counter for accumulating the number of clock pulses proportional to a time of flight (TOF), for a pulse which is emitted by the system, reflected from a point of a physical body, and detected by a focused pixel detector. The TOF data gives a direct digital scale with regard to a distance from a particular pixel to a point on the physical body at which the emitted light pulse is reflected. In a second embodiment of Patent Document 2, the counter and the high-speed clock circuit are not provided, and instead of the counter and the high-speed clock circuit, a charge accumulator and an electronic shutter (S1) are provided in each pixel detector. Each pixel detector accumulates charges, and its total amount gives the direct scale of the reciprocating TOF.
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