Digital pixel sensor with integrated charge transfer amplifier

• US 6,380,880 B1
• Filed: 03/30/2001
• Issued: 04/30/2002
• Est. Priority Date: 03/30/2001
• Status: Expired due to Term

• Current Assignee: Pixim, Inc. (Sony Group Corp.)
• Original Assignee: Pixim, Inc. (Sony Group Corp.)
• Inventors: Bidermann, William R.
• Primary Examiner(s): YOUNG, BRIAN K
• Application Number:
  US09/823,592
• Time in Patent Office: 396 Days
• Field of Search: 341/155, 341/169, 341/156
• US Class Current: 341/155
• CPC Class Codes: H04N 1/195 the array comprising a two-dimensional array or a combination of two-dimensional arrays

Abstract

A digital image sensor includes a sensor array of digital pixels which output digital signals as pixel data. Each of the digital pixels includes a photodetector producing an analog signal indicative of the amount of light impinging on the sensor array and a charge transfer amplifier coupled to receive the analog signal and generate an amplified pixel voltage signal. The digital image sensor further includes analog-to-digital conversion (ADC) circuits located within the sensor array. Each of the ADC circuits is connected to one or more charge transfer amplifiers of the digital pixels for converting the amplified pixel voltage signal of each digital pixel to a digitized pixel voltage signal. The charge transfer amplifier operates to increase the sensitivity of the digital image sensor. The charge transfer amplifier can be implemented as a transfer gate with a floating diffusion as a measuring capacitor.

Claims

1. A digital image sensor, comprising:

a sensor array of digital pixels, each of said digital pixels comprising;

a photodetector producing an analog signal indicative of the amount of light impinging on said sensor array; and

a charge transfer amplifier coupled to receive said analog signal and generating an amplified pixel voltage signal;

a plurality of analog-to-digital conversion (ADC) circuits located within said sensor array, each of said ADC circuits being connected to one or more charge transfer amplifier of said digital pixels for converting said amplified pixel voltage signal of each digital pixel in said sensor array to a digitized pixel voltage signal;

wherein said sensor array is fabricated in an integrated circuit.

2. The digital image sensor of claim 1, wherein said photodetector is a photogate and said charge transfer amplifier includes a transfer gate being controlled by a control signal and a floating diffusion having a capacitance much smaller than a capacitance of said photogate.

3. The digital image sensor of claim 1, further comprising:

a data memory coupled to said sensor array, having a plurality of data memory cells, each data memory cell for storing said digital pixel voltage signal from each pixel in said sensor array of pixels.

4. The digital image sensor of claim 3, further comprising:

a threshold memory coupled to said sensor array, having a plurality of threshold memory cells, each threshold memory cell for storing a threshold value for one of said digital pixels so that said digital pixel voltage signal in each of said data memory cells corresponds to said threshold value in a corresponding one of said threshold memory cells.

5. The digital image sensor of claim 4, further comprising:

a time index memory coupled to said sensor array, for storing time index values for each of said digital pixels in said sensor array.

6. The digital image sensor of claim 1, wherein said integrated circuit is fabricated with a CMOS technology.

7. The digital image sensor of claim 1, wherein each ADC circuit in said sensor array is connected to one charge transfer amplifier of a digital pixel in said sensor array.

8. The digital image sensor of claim 1, wherein each ADC circuit in said sensor array is connected to at least four charge transfer amplifiers of four digital pixels in said sensor array, and said each ADC circuit multiplexes between said four charge transfer amplifiers for converting said amplified pixel voltage signal of each one of said four charge transfer amplifiers to said digital pixel voltage signal.

9. The digital image sensor of claim 8, wherein each ADC circuit includes a multiplexer coupled to select one of said amplified pixel voltage signals of said four charge transfer amplifiers, said multiplexer being incorporated in a comparator of said ADC circuit.

10. The digital image sensor of claim 9, wherein each of said amplified pixel voltage signals is coupled to a gate terminal of a transistor in an input signal path of said comparator.

11. The digital image sensor of claim 1, wherein each ADC circuit in said sensor array employs a Multi-Channel Bit Serial analog-to-digital conversion technique.

12. A method for generating electrical signals representing an optical image, comprising:

generating an analog signal at a photodetector at each pixel location in a sensor array of photodetectors within a digital image sensor, said analog signal corresponding to a light intensity impinging on said pixel location;

amplifying said analog signal at each pixel location; and

converting said amplified analog signal to digital signals at each pixel location within said sensor array of photodetectors such that each pixel location provides digital output signals representing a level of said analog signal.

13. The method of claim 12, wherein said amplifying comprises:

transferring electrical charge accumulated by said photodetector at each pixel location to a measuring node, said measuring node having a smaller capacitance value than a capacitance value of said photodetector.

14. The method of claim 12, wherein an analog-to-digital conversion circuit is located within each pixel location.

15. The method of claim 12, wherein an analog-to-digital conversion circuit is associated with a group of pixel locations, and said converting said amplified analog signal comprises:

converting said amplified analog signal to digital signals at each pixel location of said group of pixel locations such that each pixel location provides digital output signals representing a level of said analog signal.

16. The method of claim 12, wherein said converting said amplified analog signal to digital signals at each pixel location uses a Multi-Channel Bit Serial analog-to-digital conversion technique.