Low-noise active pixel sensor for imaging arrays with global reset

• US 6,493,030 B1
• Filed: 04/08/1998
• Issued: 12/10/2002
• Est. Priority Date: 04/08/1998
• Status: Expired due to Term

• Current Assignee: RE Secured Networks LLC
• Original Assignee: Pictos Technologies Inc. (f/k/a Imperium IP Holdings (Cayman), Ltd.) (Imperium (IP) Holdings Incorporated)
• Inventors: Kozlowski, Lester J., Standley, David L.
• Primary Examiner(s): VU, NGOC YEN T
• Application Number:
  US09/057,202
• Time in Patent Office: 1,707 Days
• Field of Search: H04/N.314, H04/N.964, 250/208.1, 250/214.1, 250/214.R, 348/207, 348/241, 348/250, 348/294, 348/296, 348/303, 348/307, 348/312, 348/315
• US Class Current: 348/310
• CPC Class Codes: H01L 27/14609 Pixel-elements with integrated switching, control, storage or amplification elements scanning details of imagers (circuitry of solid-state image sensors H04N25/00); circuitry of imagers H04N25/70
• CPC Class Codes: H03F 2200/372 Noise reduction and elimination in amplifier
• CPC Class Codes: H03F 3/082 with FET's H03F3/085 takes precedence
• CPC Class Codes: H04N 25/575 with a response composed of multiple slopes
• CPC Class Codes: H04N 25/65 applied to reset noise, e.g. KTC noise related to CMOS structures by techniques other than CDS
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components

Abstract

An imaging array of active pixel sensors uses a reset amplifier in each pixel in a four transistor CMOS implementation. The reset amplifier acts as a variable resistance in the source-follower amplifier feedback circuit. The variable resistance is controlled by a range reset voltage applied to the reset amplifier thereby nulling the photodiode reset noise. The ramp reset voltage is applied to all reset amplifiers of all pixels at the same time, thereby providing for reset of the entire array at the same time, i.e., global reset.

Claims

1. An active-pixel sensor including a radiation detector in a plurality of active-pixel sensors organized into a sensor array, said active-pixel sensor comprising:

a transistor amplifier having an input and an output, its input connected to said radiation detector for generating an electrical signal output having a magnitude that is a function of the charge input from the radiation detector;

a first switch connected to said transistor amplifier for impressing the electrical signal from said transistor amplifier onto an output line;

a variable resistance connected between said transistor amplifier and said radiation detector for resetting the charge input of said transistor amplifier to a predetermined signal level; and

a second switch connected to said transistor amplifier and said variable resistance for providing a current source to said transistor amplifier during reset.

2. The active-pixel sensor of claim 1 wherein said first switch comprises a transistor with a first leg, a second leg and a gate, the transistor being connected between said transistor amplifier output and the output line by its first and second legs, a row select signal on the gate turning the transistor on.

3. The active-pixel sensor of claim 1 wherein said second switch comprises a transistor with a first leg, a second leg and a gate, the transistor being connected to said variable resistance and said transistor amplifier by the first leg and to a voltage source by the second leg.

4. The active-pixel sensor of claim 1 wherein said variable resistance comprises a transistor with a first leg, a second leg and a gale, the transistor connected between said transistor amplifier and said radiation detector by its first and second legs, a tapered reset supply voltage being supplied to its gate.

5. The active-pixel sensor of claim 4 wherein the tapered reset supply voltage supplied to the gate of the transistor comprises a decreasing ramp waveform commensurately increasing the series resistance of the transistor, whereby reset noise in the sensor is nulled.

6. The active-pixel sensor of claim 1 where said transistor amplifier is a MOSFET.

7. The active-pixel sensor of claim 6 wherein said first switch is a MOSFET.

8. The active-pixel sensor of claim 7 wherein said variable resistance is a MOSFET.

9. The active-pixel sensor of claim 8 wherein said radiation detector is a photodiode.

10. The active-pixel sensor of claim 9 wherein said second switch is a MOSFET.

11. An active-pixel sensor including a radiation detector in a two-dimensional array of active-pixel sensors organized into rows and columns of sensors, comprising:

a transistor amplifier having an input and an output, its input connected to said radiation detector for generating an electrical signal output having a magnitude that is a function of the charge at its input generated by the radiation detector;

a first switch connected to said transistor amplifier for impressing the electrical signal of its output onto a column output line;

a variable resistance connected between said transistor amplifier and said radiation detector for resetting the charge at said transistor amplifier input to a predetermined signal level; and

a second switch connected to said transistor amplifier and said variable resistance for providing a current source to said transistor amplifier during reset.

12. The active-pixel sensor of claim 11 wherein said first switch comprises a transistor with a first leg, a second leg and a gate, the transistor being connected between the output of said transistor amplifier and the column output line by its first and second legs, a row select signal being supplied to the gate to the transistor on.

13. The active-pixel sensor of claim 11 wherein said second switch comprises a transistor with a first leg, a second leg and a gate, the transistor being connected to said transistor amplifier and said variable resistance by the first leg and to a row output line by the second leg.

14. The active-pixel sensor of claim 11 wherein said variable resistance comprises a transistor with a first leg, a second leg and a gate, the transistor being connected between said transistor amplifier and said radiation detector by the first and second legs, a tapered reset supply voltage being supplied to the gate.

15. The active-pixel sensor of claim 12 wherein the tapered reset supply voltage supplied to the gate of the transistor comprises a decreasing ramp waveform commensurately increasing the series resistance of the transistor, whereby reset noise in the sensor is nulled.

16. The active-pixel sensor of claim 11 wherein said variable resistance is gradually increased during reset, whereby reset noise in the sensor is nulled.

17. The active-pixel sensor of claim 15 further comprising a source supply connected to the column output line of a two-dimensional array of active-pixel sensor organized into rows and columns of sensors.

18. The active-pixel sensor of claim 17 wherein said source supply comprises:

a voltage source V_SRC;

a current source I_SRC; and

means for connecting the voltage source V_SRC to said column output line during reset of the sensor, and connecting said current source I_SRC to said column output line during readout of the sensor.

19. The active-pixel sensor of claim 16 wherein said second switch comprises a transistor with a first leg, a second leg and a gate, the transistor being connected to said transistor amplifier and said variable resistance by the first leg and to a row output line by the second leg.

20. The active-pixel sensor of claim 19 wherein the second switch transistor connects a current source to said row output line during reset of the sensors, and a voltage source to said row output line during readout of the sensors.