Method for temperature compensation of an image detector

• US 6,737,654 B2
• Filed: 06/27/2002
• Issued: 05/18/2004
• Est. Priority Date: 12/28/1999
• Status: Expired due to Fees

• Current Assignee: Trixell S.A.S. (Thales SA)
• Original Assignee: Trixell S.A.S. (Thales SA)
• Inventors: Ducourant, Thierry
• Primary Examiner(s): Lee, John R.
• Assistant Examiner(s): Gill, Erin-Michael
• Application Number:
  US10/149,451
• Publication Number:
  US 20020190216A1
• Time in Patent Office: 691 Days
• Field of Search: 250/370.11, 250/370.08, 348/245
• US Class Current: 250/370.11
• CPC Class Codes: H04N 25/626 Reduction of noise due to residual charges remaining after image readout, e.g. to remove ghost images or afterimages
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/673 by using reference sources
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors

Abstract

A method and device for temperature compensation of an image detector including photosensitive spots sensitive to ambient temperature, each connected to a row conductor and a column conductor. The photosensitive spots are connected by their conductors to a read circuit. The photosensitive spots are divided into detecting photosensitive spots to be exposed to light information corresponding to the image to be detected, the read circuits associated with these photosensitive spots each delivering a measurement voltage representative of the image to be detected, and into blind photosensitive spots protected from the light information, the read circuits associated with these blind photosensitive spots each delivering a dark voltage serving for temperature compensation. During detection of an image the dark voltages are picked up, then an average correction value from the dark voltages coming from one or more detected images is generated, and the average correction value is used to generate a correction voltage to be applied, during detection of a subsequent image, to the read circuits associated with the detecting photosensitive spots so that they deliver a measurement voltage made substantially independent of temperature. Such a method and device may find application in particular to radiological image detectors.

Claims

1. A method for temperature compensation of an image detector including photosensitive spots sensitive to ambient temperature, each connected to a row conductor and a column conductor, each of the photosensitive spots being connected by one conductor to a read circuit, wherein the photosensitive spots are divided into a) detecting photosensitive spots configured to be exposed to light information corresponding to the image to be detected, read circuits associated with the detecting photosensitive spots each delivering a measurement voltage representative of the image to be detected, and b) into blind photosensitive spots protected from the light information, read circuits associated with the blind photosensitive spots each delivering a dark voltage serving for temperature compensation, comprising:

picking up, during detection of an image, the dark voltages;

generating an average correction value from the dark voltages coming from one or more detected images; and

using the average correction value to generate a correction voltage to be applied, during detection of a subsequent image, to the read circuits associated with the detecting photosensitive spots so that they deliver a measurement voltage made substantially independent of temperature.

2. The method for temperature compensation of an image detector as claimed in claim 1, further comprising:

converting, in an analog-to-digital converter, the measurement voltages and dark voltages of the photosensitive spots; and

generating the average correction value from the digitized dark voltages, the average correction value serving to control a digital-to-analog converter that delivers the correction voltage to be applied to the read circuits associated with the detecting photosensitive spots.

3. The method for temperature compensation of an image detector as claimed in claim 1, wherein the generating the average correction value includes a simple averaging over dark voltages coming from plural detected images.

4. The method for temperature compensation of an image detector as claimed in claim 1, wherein the generating the average correction value includes a sliding averaging over the dark voltages coming from plural detected images.

5. The method for temperature compensation of an image detector as claimed in claim 1, wherein in the generating the average correction value from dark voltages coming from one or more detected images, a time interval separating detection of an earliest image from detection of a most recent image used in the averaging is less than a thermal time constant of the detector.

6. The method for temperature compensation of an image detector as claimed in claim 1, further comprising connecting the blind photosensitive spots to an outermost portion of at least one row conductor.

7. A temperature-compensated image detector including photosensitive spots, each connected to a row conductor and a column conductor, each photosensitive spot being connected by one conductor to a read circuit, wherein the photosensitive spots are divided into a) detecting photosensitive spots, configured to be exposed to light information corresponding to the image to be detected, read circuits associated with the detecting photosensitive spots each delivering a measurement voltage representative of the image to be detected, and b) into blind photosensitive spots protected from the light information, read circuits associated with the blind photosensitive spots each delivering a dark voltage used for temperature compensation, comprising:

means for picking up the dark voltages during detection of an image and for generating an average correction value from the dark voltages picked up coming from one or more detected images; and

means for generating, from the average correction value, a correction voltage configured to be applied to the read circuits associated with the detecting photosensitive spots, during detection of a compensated subsequent image, so that the detecting photosensitive spots deliver a measurement voltage made approximately independent of temperature.

8. The temperature-compensated image detector as claimed in claim 7, wherein the means for picking up the dark voltages and for generating the average correction value receives the dark voltages in digital form from at least one analog-to-digital converter placed at an output of the read circuits.

9. The temperature-compensated image detector as claimed in claim 8, wherein the means for generating the correction voltage comprises a digital-to-analog converter placed between the means for picking up the dark voltages and for generating the average correction value and the read circuits of the detecting photosensitive spots.

10. The temperature-compensated image detector as claimed in claim 7, wherein the read circuit associated with a detecting photosensitive spot includes a charge-integrating circuit comprising a capacitor, a first plate of the capacitor receiving charges from the detecting photosensitive spot by the charge conductor and a second plate of the capacitor is at the correction voltage.

11. The temperature-compensated image detector as claimed in claim 7, wherein the read circuit associated with a blind photosensitive spot includes a charge-integrating circuit comprising a capacitor, a first plate of the capacitor receiving charges from the blind photosensitive spot by the conductor and a second plate of the capacitor is at a fixed reference voltage.

12. The temperature-compensated image detector as claimed in claim 7, wherein the blind photosensitive spots are connected to an outermost portion of a row conductor.

13. The temperature-compensated image detector as claimed in claim 7, wherein the blind photosensitive spots are covered with a material opaque to the light information to which the detecting photosensitive spots are exposed.

14. The temperature-compensated image detector as claimed in claim 7, wherein the detecting photosensitive spots are covered with a scintillator material that converts X-radiation into light radiation and the blind photosensitive spots are covered with an X-ray-opaque material, the material opaque to the light information, when it is present, lying between the X-ray-opaque material and the blind photosensitive spots.