Microbolometer unit cell signal processing circuit

• US 5,489,776 A
• Filed: 08/30/1994
• Issued: 02/06/1996
• Est. Priority Date: 08/30/1994
• Status: Expired due to Term

• Current Assignee: OL Security LLC (Intellectual Ventures LLC)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Lung, Gerald
• Primary Examiner(s): Fields, Carolyn E.
• Assistant Examiner(s): Glick, Edward J.
• Application Number:
  US08/297,733
• Time in Patent Office: 525 Days
• Field of Search: 250/332, 250/338.1, 250/338.4, 250/370.08, 250/351
• US Class Current: 250/332
• CPC Class Codes: G01J 5/24 Use of specially adapted circuits, e.g. bridge circuits
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• 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

A circuit (30) for processing a signal provided by a silicon microbolometer unit cell (76). In accordance with the invention, electrical energy is applied to a first terminal of the unit cell (76) to generate first and second signals at the first terminal thereof during first and second time intervals or fields, respectively. These signals are sampled and subtracted from each other by a sampling capacitor (80) to provide a third signal which is directly proportional to a difference between the first signal and the second sampled signal. In a specific embodiment, the difference signal is amplified to provide the desired output signal. The inventive circuit provides coarse DC offset non-uniformity correction and sets the overall gain of a focal plane array of silicon microbolometer unit cell detectors. This allows for use of a simplified analog signal processing circuit.

Claims

1. A circuit for processing a signal provided by a microbolometer unit cell comprising:

first means for selectively applying electrical energy to a first terminal of the unit cell to generate first and second signals at the first terminal thereof during first and second time intervals, said first means including a current source and a first switch for selectively connecting the current source to the first terminal of the unit cell;

second means for sampling the first signal during the first time interval and for sampling the second signal during the second time interval to provide first and second sampled signals respectively, said second means including a second switch having a first terminal connected to the first terminal of the unit cell; and

third means for providing a third signal which is directly proportional to a difference between the first sampled signal and the second sampled signal, said third means including a capacitor having a first terminal connected to a second terminal of the second switch.

2. The invention of claim 1 further including fourth means for amplifying the difference between the first sampled signal and the second sampled signal.

3. The invention of claim 2 wherein the fourth means includes an amplifier, and wherein a second terminal of the capacitor is connected to a first input terminal of the amplifier.

4. The invention of claim 3 further including a third switch connected across an output terminal of the amplifier and the first input terminal thereof.

5. The invention of claim 4 further including a second capacitor connected across the output terminal of the amplifier and the first input terminal thereof.

6. The invention of claim 3 further including fifth means for selectively connecting a noise limiting element to the first terminal of the unit cell.

7. The invention of claim 6 wherein the third means includes a fourth switch for connecting a third capacitor to the first terminal of the unit cell.

8. The invention of claim 7 further including means for selectively controlling the first, second, and third switches to sample the signals at the first terminal of the unit cell during consecutive fields to create a field to field difference signal for amplification by the and amplifier.

9. A night vision camera comprising:

an array of microbolometer unit cells;

a plurality of unit cell signal processing circuits, one for each unit cell, each circuit including;

a current source,

a first switch for coupling said current source to a first terminal of an associated unit cell to generate first and second signals at the first terminal thereof during first and second time intervals,

sampling means for sampling the first signal during the first time interval and for sampling the second signal during the second time interval to provide first and second sampled signals respectively, said sampling means including a second switch having a first terminal connected to the first terminal of the unit cell,

means providing a third signal which is directly proportional to a difference between the first sampled signal and the second sampled signal, said means including a capacitor having a first terminal connected to a second terminal of the second switch, and

amplifying means for amplifying the difference between the first sampled signal and the second sampled signal; and

means for displaying the amplified difference signals.