Delta-sigma digital radiometric system

Patent metadata

Field	Value
Publication number	US-9983304-B2
Application number	US-201514627094-A
Country	US
Kind code	B2
Filing date	Feb 20, 2015
Priority date	Feb 20, 2015
Publication date	May 29, 2018
Grant date	May 29, 2018

Abstract

A passive radiometric system for thermally imaging objects in a scene. The system includes a digital square-law quantizer circuit including a plurality of comparators and a voltage divider network having a plurality of resistors. Each comparator receives a different reference signal generated by the voltage divider network and a common power signal from an antenna and outputs a high or low digital bit signal. The system also includes a delta-sigma circuit having a weighting table responsive to the digital bit signals from the comparators that converts the digital bit signals to a normalized bit word. The delta-sigma circuit also includes an accumulator that receives the digital bit words from the weighting table and provides an average of the digital bit words. The system also includes a digital-to-analog converter that converts the averaged bit words to an analog signal that is provided as a feedback signal to the quantizer circuit.

First claim

What is claimed is:

1. A passive radiometric system for thermally imaging objects in a scene, said system comprising:
an antenna for receiving signals from the scene and providing a power signal;
a digital square-law quantizer circuit including four comparators each having first and second inputs, said square-law quantizer circuit further including a voltage divider network having four weighted resistors and receiving an analog feedback signal, where each resistor in the voltage divider network has a different resistance value, and wherein each comparator receives a different voltage divided signal from the voltage divider network at the first input and the power signal from the antenna at the second input and outputs a high or low digital bit signal depending on whether the power signal is greater than or less than the voltage divided signal;
a delta-sigma circuit including a weighting table responsive to the digital bit signals from the comparators, said weighting table normalizing the digital bit signals to a digital bit word having a value within a normalized range, said delta-sigma circuit further including an accumulate and decimate circuit receiving the digital bit words from the weighting table and accumulating the digital words over a predetermined sample time and dividing the accumulated digital bit words by a number of sample periods to provide an average of the digital word that is a temperature representation of the power signal; and
a digital-to-analog converter (DAC) receiving the averaged digital bit word from the accumulate and decimate circuit and converting the averaged digital bit word to an analog signal provided as the feedback signal to the voltage divider network.

2. The system according to claim 1 wherein the digital square-law quantizer circuit and the delta-sigma circuit are fabricated in silicon-germanium (SiGe) or Si complementary metal oxide semiconductor (CMOS) fabrication technologies.

3. The system according to claim 2 wherein the square-law quantizer circuit and the delta-sigma circuit are integrated on a common chip.

4. The system according to claim 1 wherein the antenna is configured to receive signals in the RF band.

5. The system according to claim 4 wherein the RF band is the W-band (94 GHz) or D-band (140 GHz).

6. The system according to claim 1 further comprising a low noise amplifier (LNA) receiving the power signal from the antenna and amplifying the power signal.

7. The system according to claim 6 further comprising a down-converter circuit receiving the power signal from the LNA and down-converting the power signal before it is applied to the digital square-law quantizer circuit.

8. A passive radiometric system for thermally imaging objects in a scene, said system comprising:
an antenna for receiving signals from the scene and providing a power signal;
a digital square-law quantizer circuit responsive to the power signal from the antenna and an analog feedback signal, said quantizer circuit converting the power signal to a digital signal, wherein the digital square-law quantizer circuit includes a plurality of comparators each having first and second inputs, said square-law quantizer circuit further including a voltage divider network having a plurality of weighted resistors and receiving the analog feedback signal, where each resistor in the voltage divider network has a different resistance value, wherein each comparator receives a different voltage divided signal from the voltage divider network at the first input and the power signal from the antenna at the second input and outputs a high or low digital bit signal depending on whether the power signal is greater than or less than the voltage divided signal, and where the combination of the digital bits from the comparators is the digital signal from the quantizer circuit;
a delta-sigma circuit responsive to the digital signals from the quantizer circuit, said delta-sigma circuit including a time-averaging device for removing signal noise by providing an average over time of the digital signals that is a temperature representation of the power signal; and
a digital-to-analog converter (DAC) receiving the averaged digital signal from the delta-sigma circuit and converting the averaged digital signal to an analog signal provided as the feedback signal to the quantizer circuit.

9. The system according to claim 8 wherein the delta-sigma circuit includes a weighting table responsive to the digital bit signals from the quantizer circuit, said weighting table normalizing the digital bit signals to a digital bit word having a value within a normalized range, said delta-sigma circuit further including an accumulate and decimate circuit receiving the digital bit words from the weighting table and accumulating the digital words over a predetermined sample time and dividing the accumulated digital bit words by a number of sample periods to provide the average of the digital signals.

10. The system according to claim 8 wherein the digital square-law quantizer circuit and the delta-sigma circuit are fabricated in silicon-germanium (SiGe) or Si complementary metal oxide semiconductor (CMOS) fabrication technologies.

11. The system according to claim 10 wherein the square-law quantizer circuit and the delta-sigma circuit are integrated on a common chip.

12. The system according to claim 8 wherein the antenna is configured to receive signals in the RF band.

13. The system according to claim 12 wherein the RF band is the W-band (94 GHz) or D-band (140 GHz).

14. A method for thermally imaging objects in a scene, said method comprising:
providing an antenna for receiving signals from the scene and accepting a power signal;
converting the power signal to a digital signal in a digital square-law quantizer circuit using an analog feedback signal, wherein converting the power signal to a digital signal in a digital square-law quantizer circuit includes providing a plurality of comparators each having first and second inputs, and providing a voltage divider network having a plurality of weighted resistors that receive the analog feedback signal, where each resistor in the voltage divider network has a different resistance value, wherein each comparator receives a different voltage divided signal from the voltage divider network at the first input and the power signal from the antenna at the second input and outputs a high or low digital bit signal depending on whether the power signal is greater than or less than the voltage divided signal, where the combination of the digital bits from the comparators is the digital signal from the quantizer circuit;
averaging the digital signal over time in a delta-sigma circuit to generate an averaged digital signal that is a temperature representation of the power signal; and
converting the averaged digital signal to the analog feedback signal in a digital-to-analog converter (DAC) and providing the feedback signal to the quantizer circuit.

15. The method according to claim 14 wherein averaging the digital signal over time in a delta-sigma circuit includes providing a weighting table responsive to the digital bit signals from the quantizer circuit, said weighting table normalizing the digital bit signals to a digital bit word having a value within a normalized range, providing an accumulate and decimate circuit receiving the digital bit words from the weighting table and accumulating the digital words over a predetermined sample time and dividing the accumulated digital bit words by a number of sample periods to provide the averaged digital signals.

16. The method according to cl

Assignees

• Northrop Grumman Systems Corp

Inventors

• Smith Andrew D
• Gilreath Leland
• Thai Khanh

Classifications

• H03M1/365

  the voltage divider being a single resistor string · CPC title

• G01S13/89 Primary

  for mapping or imaging · CPC title

• H03M1/20

  Increasing resolution using an n bit system to obtain n + m bits · CPC title

• H03M1/48 Primary

  Servo-type converters · CPC title

• H03M1/182

  the feedback signal controlling the reference levels of the analogue/digital converter · CPC title