Infrared sensor and imager with differential ferroelectric cells
View Patent ↗A pyrometer cell comprises a first ferroelectric capacitor, a second ferroelectric capacitor, and a difference circuit for determining the difference between the polarization charge, voltage, or current between the first and second ferroelectric capacitors. The cell is pulsed a plurality of times and an integrator circuit connected to the difference circuit provides an enhanced output signal representative of the integrated difference. An infrared imager is formed by an array of the pyrometer cells, with one ferroelectric capacitor in each cell exposed to an infrared source and the other ferroelectric capacitor not exposed to the infrared source.
1. An infrared imager comprising:
an array of infrared sensor cells, each said infrared sensor cell comprising: a first ferroelectric element exposed to said source of infrared radiation; and a second ferroelectric element not exposed to said source of infrared radiation; and
an output circuit for providing an output signal indicative of the difference in polarization of said first ferroelectric element and said second ferroelectric element for each of said infrared sensor cells.
2. An infrared imager as in claim 1 wherein said output circuit comprises a first circuit portion in each of said sensor cells and a second circuit portion external to said cells.
3. An infrared imager as in claim 2 wherein said first circuit portion comprises a subtractor and said second circuit portion comprises an integrator.
4. An infrared imager as in claim 3 wherein there is one of said integrators for each column or row of said array.
5. A method of sensing the intensity level of an infrared source, said method comprising:
exposing a first ferroelectric element to said infrared source;
determining a first polarization charge of said ferroelectric element exposed to said infrared source;
determining a second polarization charge of a second ferroelectric element not exposed to said infrared source;
finding the difference between said first polarization charge and said second polarization charge; and
utilizing said difference to determine said intensity level of said infrared source;
wherein said processes determining a first polarization charge, determining a second polarization charge, and finding the difference are repeated a plurality of times to determine a plurality of said differences, and further including integrating said plurality of differences.
6. A low-noise method of sensing the intensity level of an infrared source, said method comprising:
providing a sensing circuit having a first ferroelectric element and a second ferroelectric element that are essentially equivalent with respect to noise;
determining a difference between the polarization charge, voltage, or current between said first and second ferroelectric elements, which difference essentially cancels non-random noise in said sensing circuit; and
utilizing said difference to determine said intensity level of said infrared source.
7. A method as in claim 6 wherein said determining comprises sensing the difference in polarization charge between said first and second ferroelectric elements.
8. A method as in claim 7 wherein said determining comprises exposing said first ferroelectric element to said infrared source while not so exposing said second ferroelectric element.
9. A method as in claim 7 wherein said ferroelectric elements are ferroelectric capacitors.
10. A method as in claim 7 wherein said sensing circuit comprises an integrator and said utilizing comprises integrating said difference over a plurality of sensing cycles.
11. A method as in claim 7 wherein said determining further comprises reducing the random noise in said sensing circuit by determining said difference over a plurality of measurement cycles.
12. A method as in claim 11 wherein there are 150 or more of said measurement cycles.