Gain calibration for an imaging system

• US 10,128,808 B2
• Filed: 03/09/2017
• Issued: 11/13/2018
• Est. Priority Date: 08/20/2014
• Status: Active Grant

• Current Assignee: Seek Thermal, Inc.
• Original Assignee: Seek Thermal, Inc.
• Inventors: Wolfe, Jason, Parrish, William J., Williams, Ross
• Primary Examiner(s): Bryant, Casey
• Application Number:
  US15/455,007
• Publication Number:
  US 20170179912A1
• Time in Patent Office: 614 Days
• Field of Search: None
• CPC Class Codes: G01J 1/18 using comparison with a reference electric value
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01J 2001/4406 Plural ranges in circuit, e.g. switchable ranges; Adjusting sensitivity selecting gain values
• CPC Class Codes: G01J 2001/444 Compensating; Calibrating, e.g. dark current, temperature drift, noise reduction or baseline correction; Adjusting
• CPC Class Codes: G01J 2005/0077 Imaging
• CPC Class Codes: G01J 5/22 Electrical features thereof
• CPC Class Codes: G01J 5/34 using capacitors, e.g. pyroelectric capacitors
• CPC Class Codes: G01J 5/80 Calibration using comparison with reference sources G01J5/52
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: H01G 7/00 Capacitors in which the capacitance is varied by non-mechanical means; Processes of their manufacture
• CPC Class Codes: H03G 3/3084 in receivers or transmitters for electromagnetic waves other than radiowaves, e.g. lightwaves H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H04N 23/23 from thermal infrared radiation
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 25/673 by using reference sources
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors
• 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 imaging system includes an array of photodetectors and electronic circuitry associated with the photodetectors to read intensity values from the photodetectors. The electronic circuitry can include an integrator with an integrator capacitor having a nominal capacitance, wherein a gain of the electronic circuitry associated with a photodetector can depend at least in part on the actual capacitance of the integrator capacitor, the actual capacitance differing from the nominal capacitance. The imaging system can be configured to determine a gain factor that depends at least in part on the actual capacitance and/or a signal voltage input to the integrator. The imaging system can be configured to apply the gain factor based at least in part on the actual capacitance of the integrator capacitor calculated. The imaging system can be a thermal imaging system and may include an infrared camera core.

Claims

1. A method for calibration of a circuit on a microfabricated chip, the circuit comprising a capacitor having a nominal capacitance, wherein an input/output relationship of the circuit is based on the nominal capacitance of the capacitor and is used by a processing system, the method comprising:

measuring an actual output signal of the circuit as a function of an input voltage of the circuit during calibration of the circuit;

determining an actual input/output relationship between the actual output signal of the circuit and an actual capacitance of the capacitor, based on determining the actual capacitance as a function of the input voltage during calibration; and

modifying the nominal capacitance contribution to the input/output relationship used by the processing system using the actual capacitance, wherein the output signal is an input to determining the actual capacitance during operation of the circuit,

wherein the actual capacitance of the capacitor is variable based on a voltage across the capacitor, the voltage across the capacitor being based at least in part on the input voltage of the circuit.

2. The method of claim 1, wherein determining the actual capacitance comprises:

varying the input voltage over a plurality of known values;

observing the output signal at the plurality of input voltages;

comparing the output signal to an expected output signal corresponding to the nominal capacitance; and

calculating the actual capacitance as a function of the output signal.

3. The method of claim 2, wherein determining the actual capacitance further comprises fitting a curve to the determined actual capacitance as a function of the output signal.

4. The method of claim 1 further comprising developing a look up table that indexes the actual input/output relationship to the actual output signal, wherein the look up table is based on modification of the input/output relationship due to the actual capacitance.

5. The method of claim 1, wherein the actual input/output relationship is updated on a substantially continuous basis during operation of the circuit.

6. A system comprising:

a microfabricated chip, the microfabricated chip having a circuit thereon, the circuit comprising a capacitor having a nominal capacitance, wherein an input/output relationship of the circuit is based on the nominal capacitance; and

a processor in communication with the microfabricated chip and configured to use the input/output relationship of the circuit, wherein the system is configured to calibrate the circuit by;

measuring an actual output signal of the circuit of the circuit as a function of an input voltage of the circuit during calibration of the circuit;

determining an actual input/output relationship between the actual output signal of the circuit and an actual capacitance of the capacitor, based on determining the actual capacitance as a function of the input voltage during calibration; and

modifying the nominal capacitance contribution to the input/output relationship used by the processor using the actual capacitance, wherein the output signal is an input to determining the actual capacitance during operation of the circuit,

wherein the actual capacitance of the capacitor is variable based on a voltage across the capacitor, the voltage across the capacitor being based at least in part on the input voltage of the circuit.

7. The system of claim 6, wherein determining the actual capacitance comprises:

varying the input voltage over a plurality of known values;

observing the output signal at the plurality of input voltages;

comparing the output signal to an expected output signal corresponding to the nominal capacitance; and

calculating the actual capacitance as a function of the output signal.

8. The system of claim 7, wherein determining the actual capacitance further comprises fitting a curve to the determined actual capacitance as a function of the output signal.

9. The system of claim 6, wherein the processor is further configured to develop a look up table that indexes the actual input/output relationship to the actual output signal, wherein the look up table is based on modification of the input/output relationship due to the actual capacitance.

10. The system of claim 6, wherein the actual capacitance of the capacitor is variable based on a voltage across the capacitor, the voltage across the capacitor being based at least in part on the input voltage of the circuit.

11. The system of claim 6, wherein the processor is configured to calibrate the circuit on a substantially continuous basis during operation of the circuit.

12. The system of claim 6, wherein the circuit is one of a plurality of circuits on the microfabricated chip, each of the plurality of circuits comprising a capacitor having a nominal capacitance and an input/output relationship based on the nominal capacitance.

13. The system of claim 12, wherein the processor is configured to individually calibrate each of the plurality of circuits.