Multipurpose readout integrated circuit with in cell adaptive non-uniformity correction and enhanced dynamic range

• US 6,040,568 A
• Filed: 05/06/1998
• Issued: 03/21/2000
• Est. Priority Date: 05/06/1998
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Schlesselmann, John D., Caulfield, John T., Pettijohn, Kevin L., Wyles, Richard H.
• Primary Examiner(s): ALLEN, STEPHONE B
• Application Number:
  US09/073,408
• Time in Patent Office: 685 Days
• Field of Search: 250/208.1, 250/216, 250/332, 250/338.1, 250/338.4, 250/339.02, 250/349, 250/370.08, 348/164, 348/166, 348/301, 348/294, 348/311
• US Class Current: 250/208.1
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H04N 25/20 for transforming only infrared radiation into image signals
• CPC Class Codes: H04N 25/67 applied to fixed-pattern noise, e.g. non-uniformity of response
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

An IR-FPA (10) having a plurality of radiation detectors (2a) and a multipurpose ROIC (2) is disclosed. The radiation detectors (2a) are organized as a two dimensional array. The multipurpose ROIC (2) includes a plurality of readout circuit unit cells, individual ones of which are coupled to individual radiation detectors (2a) for receiving electrical signals therefrom. Each of the readout circuit unit cells operates in one of a first mode to provide a corrected m frame averaged output signal (Vout_THPF) or, a second mode to provide a subframed averaged output signal (Vout₂). In the first operating mode, a high pass filtering circuit subtracts a low frequency charge pedestal from the electrical signal to form the corrected m frame averaged output (Vout_THPF). Also disclosed is a method for operating an array of radiation detectors (2a) which includes the steps of: within a sampling period that defines a frame comprised of subframe periods, generating an electrical signal in individual ones of the radiation detectors, the electrical signals being generated in response to incident radiation; in a first operating mode, forming a high pass filtered output signal (Vout_THPF) from electrical signals generated during at least one frame period; in a second operating mode, forming a subframe averaged output signal (Vout₂) from electrical signals generated during a frame period; and reading out, in the first operating mode, the high pass filtered output signal (Vout_THPF) or, in the second operating mode, the subframe averaged output signal (Vout₂).

Claims

1. A method for operating an array of radiation detectors, comprising the steps of:

during a sampling period that defines a frame comprised of subframe periods, generating an electrical signal in individual ones of the radiation detectors, the electrical signals being generated in response to incident radiation;

in a first operating mode, forming a high pass filtered output signal from electrical signals generated during at least one frame period;

in a second operating mode, forming a subframe averaged output signal from electrical signals generated during a frame period; and

reading out, in the first operating mode, the high pass filtered output signal or, in the second operating mode, the subframe averaged output signal.

2. A method as set forth in claim 1, wherein the array of radiation detectors is organized as a two dimensional array having rows and columns, and wherein the step of reading out one of the high pass filtered output signal or the subframe averaged output signal further comprises the step of reading out the output signal on a row-by-row basis.

3. A method as set forth in claim 1, wherein in the second operating mode, the method further comprises the steps of:

in the frame period, integrating the generated electrical signal with a subframe averaging circuit during a plurality of subframe periods; and

at the conclusion of the plurality of subframe periods, averaging the integrated electrical signal to form the subframe averaged output signal.

4. A method as set forth in claim 1, wherein the frame period is about 16.67 msec and there are up to about 64 subframe periods within each of the frame periods.

5. A method as set forth in claim 1, wherein in the first operating mode, the method further comprises the steps of:

during the at least one frame period, integrating the generated electrical signal with an averaging circuit;

during a predetermined frame period, averaging the integrated electrical signal to form an averaged charge signal; and

subtracting the averaged charge signal from a currently generated electrical signal to form the high pass filtered output signal.

6. A method as set forth in claim 5, wherein the averaged charge signal is comprised of a low frequency charge pedestal.

7. A method as set forth in claim 5, wherein the predetermined frame period is comprised of a frame period which occurs once every m frame periods.

8. A method as set forth in claim 7, wherein the mth frame period is comprised of a frame period which occurs within a range of about 1-8 frame periods.

9. A method for operating an array of radiation detectors, comprising the steps of:

during a frame period comprised of subframe periods, generating an electrical signal in individual ones of the radiation detectors, the electrical signals being generated in response to incident radiation;

in a first operating mode, integrating the generated electrical signal with an averaging circuit during at least one frame period, and at a predetermined frame period, averaging and subtracting the integrated electrical signals from a currently generated electrical signal to form a high pass filtered output signal;

in a second operating mode, integrating the generated electrical signal during the subframe periods, and at the conclusion of the subframe periods, averaging the integrated electrical signal to form a subframe averaged output signal; and

reading out, in the first operating mode, the high pass filtered output signal or, in the second operating mode, the subframe averaged output signal.

10. A readout integrated circuit (ROIC) for coupling to a plurality of radiation detectors each of which outputs an electrical signal having a magnitude that is a function of an amount of radiation that is detected by said radiation detector, said ROIC comprising a plurality of readout circuit unit cells individual ones of which have an input that is switchably coupled to an associated one of said radiation detectors for receiving said electrical signals therefrom;

wherein each of said readout circuit unit cells operates in one of a first mode to provide a corrected m frame averaged output signal and a second mode to provide a subframe averaged output signal.

11. A readout integrated circuit as set forth in claim 10, wherein each of said electrical signals is comprised of a desired signal component and a low frequency charge pedestal, and wherein a magnitude of said low frequency charge pedestal is approximately equal to a charge integrated and averaged within each of said readout circuits.

12. A readout integrated circuit as set forth in claim 10, wherein said plurality of readout circuit unit cells a reintegrated upon a common substrate with said plurality of radiation detectors.

13. A readout integrated circuit as set forth in claim 10, wherein said plurality of radiation detectors are formed upon a first substrate and said plurality of readout circuit unit cells are formed upon a second substrate, and wherein said first substrate is hybridized with said second substrate.

14. A readout integrated circuit as set forth in claim 10, wherein in said first operating mode each of said readout circuit unit cells further comprises:

an averaging circuit having an input switchably coupled to said associated radiation detector and providing an averaged charge signal; and

a high pass filtering circuit having inputs switchably coupled to said averaging circuit and providing said corrected m frame averaged output signal;

wherein said high pass filtering circuit subtracts said averaged charge signal from said electrical signals to form said corrected m frame averaged output signal.

15. A readout integrated circuit as set forth in claim 14, wherein said averaging circuit further comprises:

an integration stage having at least one transistor electrically coupled to at least one integration capacitor;

a sample and hold stage having at least one transistor electrically coupled to at least one sample and hold capacitor, wherein said sample and hold stage is electrically coupled to said integration stage; and

an averaging stage having at least one transistor electrically coupled to at least one charge averaging capacitor, wherein said averaging stage is electrically coupled to said sample and hold stage, and wherein said charge averaging capacitor holds said averaged charge signal.

16. A readout integrated circuit as set forth in claim 15, wherein charge of said averaged charge signal is averaged at a frequency set by a ratio of said sample and hold capacitor to said charge averaging capacitor, and said frequency at which said at least one transistor of said averaging stage is switched.

17. A readout integrated circuit as set forth in claim 14, wherein said high pass filtering circuit further comprises:

a first buffer amplifier having an input and an output, wherein said input is electrically coupled to a sample and hold stage;

a second buffer amplifier having an input and an output, wherein said input is electrically coupled to an averaging stage; and

a differencing operational amplifier having two inputs and an output such that a first input is electrically coupled to said output of said first buffer amplifier and a second input is electrically coupled to said output of said second buffer amplifier, wherein said output of said differencing operational amplifier provides said corrected m frame averaged output signal.

18. A readout integrated circuit as set forth in claim 17, wherein said output of said differencing operational amplifier is provided by subtracting said averaged charge signal from said electrical signals in accordance with the following equation:

##EQU5## where;

V2 is a voltage measured at a node of said sample and hold stage;

V3 is a voltage measured at a node of said averaging stage;

C_SH is a capacitance measured across at least one sample and hold capacitor of said sample and hold stage;

C_AVG is a capacitance measured across at least one charge averaging capacitor of said averaging stage;

n is an index tracking a current sampled frame number; and

m is a number of delay periods during which said capacitance measured across said sample and hold capacitor is sampled onto said charge averaging capacitor.

19. A readout integrated circuit as set forth in claim 14, wherein said high pass filtering circuit further comprises:

a first buffer amplifier having an input and an output, wherein said input is electrically coupled to an integration stage;

a second buffer amplifier having an input and an output, wherein said input is electrically coupled to an averaging stage; and

a differencing operational amplifier having two inputs and an output such that a first input is electrically coupled to said output of said first buffer amplifier and a second input is electrically coupled to said output of said second buffer amplifier, wherein said output of said differencing operational amplifier provides said corrected m frame averaged output signal.

20. A readout integrated circuit as set forth in claim 19, wherein said output of said differencing operational amplifier is provided by subtracting of said averaged charge signal from said electrical signals in accordance with the following equation:

##EQU6## where;

V1 is a voltage measured at a node of said integration stage;

V2 is a voltage measured at a node of a sample and hold stage;

V3 is a voltage measured at a node of said averaging stage;

C_SH is a capacitance measured across at least one sample and hold capacitor of said sample and hold stage;

C_AVG is a capacitance measured across at least one charge averaging capacitor of said averaging stage;

n is an index tracking a current sampled number; and

m is a number of delay periods during which said capacitance measured across said at least one sample and hold capacitor is sampled onto said at least one charge averaging capacitor.