Pixel structure, image sensor device and system with pixel structure, and method of operating the pixel structure

Abstract

A photodetector in semiconductor material is provided with a first transfer gate between the photodetector and a first diffusion region in the semiconductor material, a second transfer gate between the photodetector and a second diffusion region in the semiconductor material, a capacitor connected between the first diffusion region and the second diffusion region, a first switch connected between the first diffusion region and a first reference voltage, and a second switch connected between the second diffusion region and a second reference voltage.

We claim: 
     
         1 . A pixel structure for a semiconductor imaging device, comprising:
 a photodetector in a semiconductor material,   a first transfer gate between the photodetector and a first diffusion region in the semiconductor material,   a second transfer gate between the photodetector and a second diffusion region in the semiconductor material,   a capacitor connected between the first diffusion region and the second diffusion region,   a first switch connected between the first diffusion region and a first reference voltage,   a second switch connected between the second diffusion region and a second reference voltage, and   buffer amplifiers connected to the first diffusion region and the second diffusion region.   
     
     
         2 . The pixel structure according to  claim 1 , wherein the photodetector is a pinned photodiode in a substrate comprising the semiconductor material. 
     
     
         3 . The pixel structure according to  claim 1 , wherein the first reference voltage and the second reference voltage are equal. 
     
     
         4 . The pixel structure according to  claim 3 , wherein the first reference voltage and the second reference voltage are equal to a supply voltage. 
     
     
         5 . The pixel structure according to  claim 1 , wherein the first reference voltage or the second reference voltage is connected to a supply voltage. 
     
     
         6 . The pixel structure according to  claim 1 , further comprising:
 a select transistor connected to a column bus.   
     
     
         7 . The pixel structure according to  claim 6 , further comprising:
 a source follower formed by a field-effect transistor, which is connected to the select transistor, a gate of the source follower being connected to the first diffusion region.   
     
     
         8 . An image sensor device comprising a two-dimensional array of pixel structures according to  claim 1 . 
     
     
         9 . An imaging system including an image sensor device according to  claim 8 , further comprising:
 a light source synchronized to the image sensor device, the light source being configured to be active when the signal is acquired on the first diffusion region and not active when the signal is acquired on the second diffusion region, or vice versa.   
     
     
         10 . The imaging system according to  claim 9 , wherein the light source is configured to project a pattern or sequence of patterns on a scene to be imaged. 
     
     
         11 . A method of operating the pixel structure according to  claim 1 , comprising:
 discharging the capacitor by closing both the first switch and the second switch into a connecting state,   acquiring a first signal on the photodetector and transferring the first signal to the first diffusion region by a charge transfer pulse on the first transfer gate, while the second switch is closed in a connecting state,   acquiring a second signal on the photodetector and transferring the second signal to the second diffusion region by a charge transfer pulse on the second transfer gate, while the first switch is closed in a connecting state, and after acquisition of the signals, reading the pixel signal out from the first diffusion region while the second diffusion region is connected to the second reference voltage via the second switch.   
     
     
         12 . The method according to  claim 11 , wherein the second transfer gate is at a higher electric potential than the first transfer gate during readout of the pixel signal. 
     
     
         13 . The method according to  claim 11 , wherein first and second signals are repeatedly acquired and accumulated on the capacitor. 
     
     
         14 . The method according to  claim 11 , wherein at least one of the charge transfer pulse on the first transfer gate and the charge transfer pulse on the second transfer gate is a multiple pulse. 
     
     
         15 . The method according to  claim 11 , wherein the operation of the pixel structure is synchronously performed with the operation of a structured-light projector. 
     
     
         16 . A method of operating a pixel structure, the method comprising:
 discharging a capacitor by closing both a first switch and a second switch into a connecting state, wherein the capacitor is connected between a first diffusion region and a second diffusion region, the first switch is connected between the first diffusion region and a first reference voltage, and the second switch is connected between the second diffusion region and a second reference voltage,   acquiring a first signal on a photodetector of the pixel structure, wherein the photodetector is arranged in a semiconductor material, and transferring the first signal to the first diffusion region by a charge transfer pulse on a first transfer gate, while the second switch is closed in a connecting state,   acquiring a second signal on the photodetector and transferring the second signal to the second diffusion region by a charge transfer pulse on a second transfer gate, while the first switch is closed in a connecting state, and after acquisition of the signals, reading the pixel signal out from the first diffusion region while the second diffusion region is connected to the second reference voltage via the second switch, wherein   the first transfer gate is arranged between the photodetector and the first diffusion region in the semiconductor material, and   the second transfer gate is arranged between the photodetector and the second diffusion region in the semiconductor material.   
     
     
         17 . The method according to  claim 16 , wherein the second transfer gate is at a higher electric potential than the first transfer gate during readout of the pixel signal. 
     
     
         18 . The method according to  claim 16 , wherein first and second signals are repeatedly acquired and accumulated on the capacitor. 
     
     
         19 . The method according to  claim 16 , wherein at least one of the charge transfer pulse on the first transfer gate and the charge transfer pulse on the second transfer gate is a multiple pulse. 
     
     
         20 . The method according to  claim 16 , wherein the operation of the pixel structure is synchronously performed with the operation of a structured-light projector.