DELTA-SIGMA DIGITAL RADIOMETRIC SYSTEM

摘要

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.

主权项

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 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 an analog feedback signal, 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.