Focal plane antenna to sensor interface for an ultra-sensitive silicon sensor
An electrical interface between a scene to be imaged and a bolometer type sensor is disclosed. Efficiency is improved by means of a thermal energy concentrator including a lens and an antenna. Where a plurality of bolometer pixels are located in an array, a microantenna is provided for each pixel in the array with a common lens being provided to focus and channel incoming radiation to each microantenna. Radiation from a scene is further coupled by means of a lens and microantenna to the absorbing element of each bolometer through an AC coupling circuit including an electronic chopper implemented by means of a PIN diode, the conductivity of which is varied so as to affect the reflection coefficient of the input signal supplied through the microantenna.
1. An electromagnetic radiation sensor assembly, comprising:
at least one bolometer type sensor located in a detector sub-assembly and including a thermally responsive sensing element co-located with and in thermal contact with a thermal absorber element;
a sub-assembly including an antenna for receiving incident radiant energy from a remote source of electromagnetic radiation;
one or more elements for maximizing the energy coupling between the remote source of electromagnetic energy and the thermal absorber element;
an AC coupling circuit comprising an inductive coupling circuit for providing electrical coupling and thermal isolation of the radiant energy from the antenna element to the thermal absorber element;
wherein the thermally responsive sensing element senses the temperature change in the absorber element; and
readout circuitry for providing an output signal of the temperature sensed by said sensing element.
2. A radiation sensor assembly in accordance with claim 1 wherein said AC coupling circuit additionally includes circuit means for tuning the coupling circuit to a predetermined frequency band.
3. A radiation sensor assembly in accordance with claim 1 wherein said inductive coupling circuit includes a transformer having a primary winding coupled to the antenna and a secondary winding coupled to the thermal absorber element.
4. A radiation sensor assembly in accordance with claim 3 and additionally including circuit means for providing an impedance match between the antenna and the thermal absorber element.
5. A radiation sensor assembly in accordance with claim 3 and additionally including circuit means connected to the primary winding of the transformer for tuning the AC coupling circuit to a predetermined frequency band.
6. A radiation sensor assembly in accordance with claim 5 wherein said circuit means for tuning the AC coupling circuit comprises capacitance circuit means.
7. A radiation sensor assembly in accordance with claim 6 wherein said capacitance circuit means includes capacitance circuit means connected between the antenna and the primary winding of the transformer.
8. A radiation sensor assembly in accordance with claim 7 wherein said capacitance circuit means comprises at least one tuning capacitor connected in series with the primary winding of the transformer.
9. A radiation sensor assembly in accordance with claim 8 and additionally including a switched capacitance circuit coupled across the tuning capacitor for detecting the AC coupling and thereby provide a chopper type shutter by resonance switching.
10. A radiation sensor assembly in accordance with claim 9 wherein the switched capacitance circuit includes a capacitance element connected in series with an electrical switch.
11. A radiation sensor assembly in accordance with claim 10 wherein the switch comprises a semiconductor switch.
12. A radiation sensor assembly in accordance with claim 11 wherein the semiconductor diode comprises a PIN diode.
13. A radiation sensor assembly in accordance with claim 1 and additionally including circuit means providing a shutter for interrupting the radiant energy from the antenna to the thermal absorber element.
14. A radiation sensor assembly in accordance with claim 13 wherein the shutter comprises a switch.
15. A radiation sensor assembly in accordance with claim 13 wherein the circuit means providing a shutter comprises an electronic shutter located between the antenna and the thermal absorber element.
16. A radiation sensor assembly in accordance with claim 13 wherein said circuit for providing electrical coupling includes a transformer having a primary winding coupled to the antenna and a secondary winding coupled to the thermal absorber element and wherein the shutter is connected from a circuit node between the antenna and primary winding and ground.
17. A radiation sensor assembly in accordance with claim 16 wherein said shutter means comprises switch means.
18. A radiation sensor assembly in accordance with claim 16 wherein said shutter means comprises a semiconductor diode.
19. A radiation sensor assembly in accordance with claim 18 wherein the semiconductor diode comprises a PIN diode.
20. A radiation sensor assembly in accordance with claim 13 wherein said circuit for providing electrical coupling includes a transformer having a primary winding coupled to the antenna and a secondary winding coupled to the thermal absorber element and wherein the shutter is coupled in series with the primary winding.
21. A radiation sensor assembly in accordance with claim 20 wherein said shutter means comprises switch means.
22. A radiation sensor assembly in accordance with claim 20 wherein said shutter means comprises a semiconductor diode.
23. A radiation sensor assembly in accordance with claim 22 wherein the semiconductor diode comprises a PIN diode.
24. A radiation sensor assembly in accordance with claim 1 wherein said antenna comprises a multi-terminal, self-complementary antenna structure.
25. A radiation sensor assembly in accordance with claim 24 wherein said antenna comprises a toothed log periodic multi-terminal, self-complementary antenna structure.
26. A radiation sensor assembly in accordance with claim 25 wherein said antenna comprises a two terminal antenna structure.
27. A radiation sensor assembly in accordance with claim 25 wherein said antenna comprises a three terminal antenna structure.
28. A radiation sensor assembly in accordance with claim 1 wherein said one or more elements for maximizing energy includes a lens structure in relatively close proximity to said antenna for focusing incident energy from said source onto the antenna.
29. A radiation sensor assembly in accordance with claim 28 wherein the lens structure includes a substrate affixed thereto and having an anti-reflective coating on one surface.
30. A radiation sensor assembly in accordance with claim 29 wherein the substrate is comprised of semiconductor material.
31. A radiation sensor assembly in accordance with claim 29 wherein the substrate is comprised of silicon.
32. A radiation sensor assembly in accordance with claim 1 wherein the detector sub-assembly is located in the detector stage of a three stage sensor pixel including a detector stage, an intermediate stage, and a heat bath stage, and
wherein the readout circuitry is located in the intermediate stage.
33. A radiation sensor assembly in accordance with claim 32 wherein the sub-assembly including an antenna is located on the heat bath stage.
34. A radiation sensor assembly in accordance with claim 1 wherein the detector sub-assembly is located in the detector stage of a two stage sensor pixel including a detector stage and a heat bath stage, and
wherein the readout circuitry is located in the heat bath stage.
35. A radiation sensor assembly in accordance with claim 1 wherein said at least one bolometer type sensor comprises a plurality of sensors located in respective detector sub-assemblies.
36. A radiation sensor assembly in accordance with claim 35 wherein said plurality of sensors are arranged in an array.
37. A radiation sensor assembly in accordance with claim 36 wherein each of said plurality of sensors include a separate antenna.
38. A radiation sensor assembly in accordance with claim 37 wherein the separate antenna comprises microantennas including multi-terminal, self-complementary antenna structures.