Method for temperature compensation of an image dectector

• US 20020190216A1
• Filed: 06/27/2002
• Published: 12/19/2002
• Est. Priority Date: 12/28/1999
• Status: Active Grant

• Current Assignee: Trixell S.A.S. (Thales SA)
• Original Assignee: Trixell S.A.S. (Thales SA)
• Inventors: Ducourant, Thierry
• Granted Patent: US 6,737,654 B2
• Time in Patent Office: Days
• 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

This is a method for temperature compensation of an image detector comprising photosensitive spots (O1 to O6, R1 to R9), these being sensitive to ambient temperature, each connected to a row conductor (Y1 to Y3) and a column conductor (W1, W2, Z1 to Z3). Each of the photosensitive spots is connected via one of its conductors to a read circuit (30a, 30b). The photosensitive spots are divided into detecting photosensitive spots (R1 to R9), intended to be exposed to light information corresponding to the image to be detected, the read circuits (30b) associated with these photosensitive spots each delivering a measurement voltage representative of the image to be detected, and into blind photosensitive spots (O1 to O6) protected from the light information, the read circuits (30a) associated with these blind photosensitive spots each delivering a dark voltage serving for temperature compensation. During detection of an image, the method consists in picking up the dark voltages, then in generating an average correction value from the dark voltages coming from one or more detected images and in using the average correction value to generate a correction voltage (VDR) to be applied, during detection of a subsequent image, to the read circuits (30b) associated with the detecting photosensitive spots (R1 to R9) so that they deliver a measurement voltage made substantially independent of temperature.

Application in particular to radiological image detectors.

Claims

1. A method for temperature compensation of an image detector comprising photosensitive spots (O1 to O6, R1 to R9), these being sensitive to ambient temperature, each connected to a row conductor (Y1 to Y3) and a column conductor (W1, W2, Z1 to Z3), each of the photosensitive spots being connected via one of its conductors to a read circuit (30a, 30b), characterized in that the photosensitive spots are divided into detecting photosensitive spots (R1 to R9), intended to be exposed to light information corresponding to the image to be detected, the read circuits (30b) associated with these photosensitive spots each delivering a measurement voltage representative of the image to be detected, and into blind photosensitive spots (O1 to O6) protected from the light information, the read circuits (30a) associated with these blind photosensitive spots each delivering a dark voltage serving for temperature compensation, and in that it consists, during detection of an image, in picking up the dark voltages, then in generating an average correction value from the dark voltages coming from one or more detected images and in using the average correction value to generate a correction voltage (VDR) to be applied, during detection of a subsequent image, to the read circuits (30b) associated with the detecting photosensitive spots (R1 to R9) 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, characterized in that it consists in converting, in an analog-to-digital converter (70), the measurement and dark voltages of the photosensitive spots and in generating the average correction value from the digitized dark voltages, this average correction value serving to control a digital-to-analog converter (90) which 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 either of claims 1 and 2, characterized in that it consists in generating the average correction value by a simple averaging over dark voltages coming from several detected images.

4. The method for temperature compensation of an image detector as claimed in either of claims 1 and 2, characterized in that it consists in generating the average correction value by a sliding averaging over the dark voltages coming from several detected images.

5. The method for temperature compensation of an image detector as claimed in one of claims 1 to 4, characterized in that it consists in generating the average correction value from dark voltages coming from one or more detected images, the time interval separating the detection of the earliest image from the detection of the most recent image used in the averaging being less than the thermal time constant of the detector.

6. The method for temperature compensation of an image detector as claimed in one of claims 1 to 5, characterized in that it consists in connecting the blind photosensitive spots to an outermost portion (20) of at least one row conductor (Y1 to Y3).

7. A temperature-compensated image detector comprising photosensitive spots (O1 to O6, R1 to R9), each connected to a row conductor (Y1 to Y3) and a column conductor (W1, W2, Z1 to Z3), each photosensitive spot being connected via one of its conductors to a read circuit (30a, 30b), characterized in that the photosensitive spots are divided into detecting photosensitive spots (R1, R9), intended to be exposed to light information corresponding to the image to be detected, the read circuits (30b) associated with these photosensitive spots each delivering a measurement voltage representative of the image to be detected, and into blind photosensitive spots (O1 to O6) protected from the light information, the read circuits (30a) associated with these blind photosensitive spots each delivering a dark voltage used for temperature compensation and in that it comprises 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 (VDR) intended to be applied to the read circuits (30b) associated with the detecting photosensitive spots, during detection of a compensated subsequent image, so that the detecting photosensitive spots (R1 to R9) deliver a measurement voltage made approximately independent of temperature.

8. The temperature-compensated image detector as claimed in claim 7, characterized in that the means (80) for picking up the dark voltages and for generating the average correction value receive the dark voltages in digital form from at least one analog-to-digital converter (70) placed at the output of the read circuits (30a, 30b).

9. The temperature-compensated image detector as claimed in claim 8, characterized in that the means (90) for generating the correction voltage comprise a digital-to-analog converter placed between the means for picking up the dark voltages and for generating the average correction value (80) and the read circuits (30b) of the detecting photosensitive spots.

10. The temperature-compensated image detector as claimed in one of claims 7 to 9, characterized in that the read circuit (30b) associated with a detecting photosensitive spot (R1 to R9) is a charge-integrating circuit comprising a capacitor (31b), one plate of which receives charges from the detecting photosensitive spot (R1 to R9) via the charge conductor (Z1, Z2, Z3) and the other plate of which is at the correction voltage (VDR).

11. The temperature-compensated image detector as claimed in one of claims 7 to 10, characterized in that the read circuit (30a) associated with a blind photosensitive spot (O1 to O6) is a charge-integrating circuit comprising a capacitor (31a), one plate of which receives charges from the blind photosensitive spot (O1 to O6) via the conductor (W1, W2) and the other plate of which is at a fixed reference voltage (VDR0).

12. The temperature-compensated image detector as claimed in one of claims 7 to 11, characterized in that the blind photosensitive spots are connected to an outermost portion (20) of a row conductor (Y1 to Y3).

13. The temperature-compensated image detector as claimed in one of claims 7 to 12, characterized in that the blind photosensitive spots (O1 to O6) are covered with a material (PN) opaque to the light information to which the detecting photosensitive spots are exposed, such as black paint.

14. The temperature-compensated image detector as claimed in one of claims 7 to 13, characterized in that the detecting photosensitive spots (R1 to R9) are covered with a scintillator material (SC) which converts X-radiation into light radiation and the blind photosensitive spots (O1 to O6) are covered with an X-ray-opaque material (PB) such as lead, the material (PN) opaque to the light information, when it is present, lying between the X-ray-opaque material (PB) and the blind photosensitive spots (O1 to O6).