Methods and circuitry for correcting temperature-induced errors in microbolometer focal plane array
First Claim
1. A microbolometer detector circuit comprising:
- a substrate;
a first microbolometer detector attached to said substrate;
a second microbolometer detector thermally shorted to said substrate, said second microbolometer detector being for providing temperature compensation for said first microbolometer detector;
a first voltage source, said first and second microbolometers being connected in series in a conduction path supplied by said first voltage source; and
a transistor connected between said first and second microbolometer detectors in said conduction path, a gate of said transistor being connected to a second voltage source.
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Abstract
Correction for temperature-induced non-uniformities in the response characteristics of the microbolometers in an infrared focal plane array (FPA) is performed by applying a non-uniform corrective bias to the individual microbolometers. The corrective bias is applied either before or during the bias or integration period during which the detectors are sampled. The bias-correction can be applied to two-dimensional detector multiplexers at each column amplifier input, the reference potential for each column amplifier or the voltage supply for each detector element. The magnitude of each corrective bias is determined by calibrating the detectors at different temperatures and different levels of incident infrared radiation. According to another aspect of this invention, a microbolometer which is thermally-shorted to the substrate on which the read out integrated circuit (ROIC) is formed is used along with the sensing microbolometer to compensate for variations in temperature. Circuitry for providing on-ROIC substrate temperature control is also described. This invention allows the operation of a microbolometer FPA over a wider range of device substrate temperatures and thereby significantly reduces the complexity and cost of the system as compared with the conventional technique of cooling the FPA.
88 Citations
40 Claims
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1. A microbolometer detector circuit comprising:
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a substrate; a first microbolometer detector attached to said substrate; a second microbolometer detector thermally shorted to said substrate, said second microbolometer detector being for providing temperature compensation for said first microbolometer detector; a first voltage source, said first and second microbolometers being connected in series in a conduction path supplied by said first voltage source; and a transistor connected between said first and second microbolometer detectors in said conduction path, a gate of said transistor being connected to a second voltage source. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 21)
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11. A microbolometer detector circuit comprising:
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a substrate; a first microbolometer detector thermally isolated from said substrate; and a digital-to-analog converter coupled to said first microbolometer detector for providing a bias for correcting temperature-induced variations in the properties of said first microbolometer detector. - View Dependent Claims (12, 13, 14, 15, 16)
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17. A microbolometer detector circuit comprising:
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a substrate; a first microbolometer detector thermally isolated from said substrate; a second microbolometer detector thermally shorted to said substrate; a resistor for providing thermal energy to said substrate; and a feedback circuit linking said second microbolometer detector and said resistor such that said substrate is maintained at a substantially constant temperature. - View Dependent Claims (18, 19, 20)
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22. A microbolometer focal plane array comprising:
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a substrate; an array of microbolometer cells each containing a microbolometer detector fixed to said substrate; an analog-to-digital converter for converting outputs of said microbolometer detectors into digital words; a data processor programmed to apply a correction algorithm to said digital words to generate bias correction coefficients; a correction coefficient memory for storing said bias correction coefficients; and bias correction circuitry for loading said bias correction coefficients into individual microbolometer cells. - View Dependent Claims (23, 24, 25, 26)
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27. A method of detecting the level of incident optical radiation comprising:
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providing a microbolometer detector, said microbolometer detector being attached to a substrate; applying a variable voltage bias to said microbolometer detector; and detecting the resistance of said microbolometer detector, said resistance being representative of the level of said optical radiation. - View Dependent Claims (28, 29, 30, 31, 32, 33, 34, 35, 36)
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37. A method of detecting the level of incident optical radiation comprising:
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providing an array of microbolometer detectors, said microbolometer detectors being attached to a substrate; transferring a first quantity of energy to a first microbolometer detector and a second quantity of energy to a second microbolometer detector; and detecting the resistance of each of said microbolometer detectors, said resistance being representative of the level of said optical radiation. - View Dependent Claims (38, 39, 40)
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Specification