Compact CMOS-based x-ray detector adapted for dental applications

1. An image sensor comprising:

a two-dimensional array of pixel sensors;

a layer of scintillation material adjacent to said two-dimensional array, said scintillation material emitting light in response to x-rays impinging thereon, said light being detected by said pixel sensors; and

a controller that reads out data stored in said two-dimensional array of pixel sensors and forms an image comprising a two-dimensional array of pixels therefrom, said controller correcting that data for errors resulting from x-rays that generate electrons that are stored in said pixel sensors in the process of forming said image;

wherein each of said pixel sensors comprises a photodetector that stores a charge in response to said light being received by that photodetector during a preceding time period; and

wherein said controller forms said image by causing said array of pixel sensors to form a plurality of frames, each frame comprising an array of measurements determined by said charges stored by said pixel sensors during a corresponding preceding time period; and

wherein said image comprises, for each pixel, a sum of said measurements corresponding to said charges stored by a corresponding one of said pixel sensors in at least two frames of said plurality of frames, said measurements having values less than a predetermined threshold value for each pixel sensor.

2. The image sensor of claim 1 wherein each of said pixel sensors further comprises a reset circuit, and an interface that connects that pixel sensor to said controller in response to commands generated by said controller, said reset circuit resetting said photodetector by causing a predetermined potential to be coupled to said photodetector.

3. The image sensor of claim 2 , wherein said controller causes said reset circuits to reset said photodetectors at the end of each of said frames.

4. The image sensor of claim 1 wherein said controller identifies pixel sensors in which said stored charge is greater than said threshold value.

5. The image sensor of claim 4 wherein said controller combines data from a plurality of frames for each pixel sensor to determine a corresponding pixel in said image and wherein said controller does not combine data from said identified pixel sensors in forming said image.

6. An image sensor comprising:

a two-dimensional array of pixel sensors;

a layer of scintillation material adjacent to said two-dimensional array, said scintillation material emitting light in response to x-rays impinging thereon, said light being detected by said pixel sensors; and

a controller that reads out data stored in said two-dimensional array of pixel sensors and forms an image comprising a two-dimensional array of pixels therefrom, said controller correcting that data for errors resulting from x-rays that generate electrons that are stored in said pixel sensors in the process of forming said image,

wherein said controller forms said image by causing said two-dimensional array of pixel sensors to form a plurality of frames, each frame comprising a measurement of a charge stored by each pixel sensor during a preceding time period, said controller combining data from said plurality of frames to form said image;

wherein said controller identifies pixel sensors in which said stored charge is greater than a threshold value; and

wherein said threshold value is different for different ones of said pixel sensors.

7. An image sensor comprising:

a two-dimensional array of pixel sensors;

a layer of scintillation material adjacent to said two-dimensional array, said scintillation material emitting light in response to x-rays impinging thereon, said light being detected by said pixel sensors;

a controller that reads out data stored in said two-dimensional array of pixel sensors and forms an image comprising a two-dimensional array of pixels therefrom, said controller correcting that data for errors resulting from x-rays that generate electrons that are stored in said pixel sensors in the process of forming said image,

wherein each pixel sensor further comprises:

a comparator that compares a signal voltage generated by said photodetector in said pixel with a reference voltage, said comparator generating a stop signal when said signal voltage is in a predetermined relationship with said reference voltage; and

a first counter that counts pulses from a clock input until said stop signal is generated, said first counter storing a digital count value.

8. The image sensor of claim 7 wherein said first counter is blocked from counting if said signal voltage is greater than a threshold voltage.

9. The image sensor of claim 8 wherein each pixel sensor further comprises a second counter that is incremented by a frame signal, said second counter being blocked from incrementing on said frame signal if said signal voltage is greater than said threshold voltage.

10. The image sensor of claim 9 wherein each pixel sensor further comprises a memory for storing said threshold voltage.

11. The image sensor of claim 10 wherein said memory stores a voltage on a conductor connected to said memory in response to a threshold reset signal and a determination that said second counter is set to zero.