Microbolometer focal plane array with temperature compensated bias
A microbolometer imaging apparatus having an array of selectable substrate-isolated microbolometer detectors, a detector selection controller, and a readout circuit. The detectors may be exposed to a scene of interest, and each detector has a corresponding resistor value. The detector selection controller may selectively couple an electrical bias source to each detector. The readout circuit may establish an output signal representative of the resistance value of each detector. The readout circuit includes a feedback bias control circuit modulates the electrical bias source as a function of the output signal.
1. A microbolometer imaging apparatus, comprising:
an array of selectable substrate-isolated microbolometer detectors for being exposed to a target scene of interest, each detector, D n , having corresponding resistance value, Rpixel n ;
a detector selection controller coupled to the array of detectors for selectively coupling an electrical bias source to each detector; and
a readout circuit for establishing a corresponding output signal, Sout n , representative of the resistance value, Rpixel n associated with the n th detector, D n , at a given instant, the readout circuit comprising:
a feedback bias control circuit comprising an integrating amplifier circuit that modulates the electrical bias source as a function of the microbolometer detector output signal, Sout.
2. The apparatus of claim 1 , wherein the readout circuit further includes a transimpedance amplifier for establishing the output signal, Sout n , as a function of the electrical bias source and the detector resistance, Rpixel n , for selected ones of the detectors.
3. The apparatus of claim 1 , wherein the readout circuit includes a selection switch circuit for selectively coupling the microbolometer detector output signal, Sout, with the feedback bias control circuit.
4. A microbolometer imaging apparatus, comprising:
an array of selectable substrate-isolated microbolometer detectors for being exposed to a target scene of interest, each detector, D n , having corresponding resistance value, Rpixel n ;
a detector selection controller coupled to the array of detectors for selectively coupling an electrical bias source to each detector; and
a readout circuit for establishing a corresponding output signal, Sout n , representative of the resistance value, Rpixel n associated with the n th detector, D n , at a given instant, the readout circuit comprising:
a feedback bias control circuit that modulates the electrical bias source as a function of the microbolometer detector output signal, Sout; and
a selection switch circuit for selectively coupling the microbolometer detector output signal, Sout, with the feedback bias control circuit.
5. The apparatus of claim 4 wherein the selection switch circuit comprises:
a pixel quality monitor for determining if selected detectors, D n , of the microbolometer detector array are to be included in the determination of the electrical bias source;
a pixel selection logic controller coupled to the pixel quality monitor and the detector selection controller; and
a selection switch coupled in series with the microbolometer detector output signal, Sout, and the feedback bias control circuit, the selection switch being controlled by the pixel selection logic controller.
6. The apparatus of claim 4 , wherein the readout circuit further includes a transimpedance amplifier for establishing the output signal, Sout.
7. The apparatus of claim 4 , wherein the feedback bias control circuit comprises an integrating amplifier circuit.
8. The apparatus of claim 5 , wherein the pixel quality monitor is coupled with the output signal, Sout.
9. The apparatus of claim 5 , wherein the output signal is an analog signal, and the apparatus further includes an analog-to-digital (A/D) converter for converting the output signal to a digital signal, Dout.
10. The apparatus of claim 9 , wherein the pixel quality monitor is coupled with the A/D converter.
11. A microbolometer imaging apparatus, comprising:
an array of selectable substrate-isolated microbolometer detectors for being exposed to a target scene of interest, each detector, D n , having corresponding resistance value, Rdetector n ;
at least one temperature sensor associated in thermal proximity to selected ones of rows or columns of the array, each temperature sensor, S m , having a corresponding electrical parameter value, Rsensor m ;
a detector selection controller coupled to the array of detectors and the at least one temperature sensor for selectively coupling an electrical detector-bias source to each detector and an electrical sensor-bias source to each temperature sensor; and
a readout circuit for establishing an output signal, Sout, the output signal having
(1) a detector output signal component, Sout n , representative of the resistance value, Rdetector n , associated with the n th detector, D n , at a given instant; and
(2) a sensor output signal component, Sout m , representative of the electrical parameter value, Rsensor m , associated with the m th temperature sensor, S m , at a given instant;
the readout circuit comprising:
a feedback sensor-bias control circuit that modulates the electrical sensor-bias source as a function of the sensor output signal component of the output signal Sout; and
a feedback detector-bias control circuit that modulates the electrical detector-bias source as a function of the sensor-bias source and a detector bias offset.
12. The apparatus of claim 11 , wherein the detector output signal component is representative of the resistance value, Rdetector n , associated with the n th detector, D n , at a given instant, and the electrical detector-bias source.
13. The apparatus of claim 11 , wherein the sensor output signal component signal component, Sout m , is representative of the electrical parameter value, Rsensor m , associated with the m th temperature sensor, S m , at a given instant, and the electrical sensor bias source.
14. The apparatus of claim 11 , wherein the readout circuit includes a selection switch circuit for selectively coupling the output signal, Sout, to the feedback sensor-bias control circuit.
15. The apparatus of claim 12 , wherein the coupling of the output signal is selected to couple to the sensor output signal component to the feedback sensor-bias control circuit.
16. The apparatus of claim 15 , wherein the selection switch circuit comprises:
a pixel quality monitor for determining if selected temperature sensors are to be included in the modulation of the electrical sensor-bias source;
a pixel selection logic controller coupled to the pixel quality monitor and the detector selection controller; and
a selection switch coupled in series with the output signal, Sout, and the feedback sensor-bias control circuit, the selection switch being controlled by the pixel selection logic controller.
17. The apparatus of claim 11 , wherein the readout circuit further includes a transimpedance amplifier for establishing the output signal, Sout.
18. The apparatus of claim 11 , wherein the feedback sensor-bias control circuit comprises an integrating amplifier circuit.
19. The apparatus of claim 11 , wherein the feedback detector-bias control circuit comprises a differential amplifier.
20. The apparatus of claim 12 , wherein the pixel quality monitor is coupled with the output signal, Sout.
21. The apparatus of claim 12 , wherein the output signal is an analog signal, and the apparatus further includes an analog-to-digital (A/D) converter for converting the output signal to a digital signal, Dout.
22. The apparatus of claim 17 , wherein the pixel quality monitor is coupled with the A/D converter.
23. The apparatus of claim 11 , wherein the temperature sensors comprise heat-sunk microbolometer detectors.
24. The apparatus of claim 11 , wherein the temperature sensors are thermistors.