Low-power, high-speed track-and-hold circuit for a direct-sampling digital radiometer

The National Aeronautics and Space Administration is developing instruments for the measurement of soil moisture, which is an essential component for understanding the hydrologic cycle of the Earth. It has been concluded that a synthetic thinned aperture radiometer could meet the science and hardware requirements for measuring the soil moisture within a 10-km spatial resolution. The hardware required for STAR is as many as 900 radiometers with a power-limitation of 250 mW per radiometer, which is unachievable using commercially available parts.; The proposed research addresses the power-limited environment of the STAR instrument by developing key components for a direct-sampling digital radiometer, which omits the mixer and local oscillator of the superheterodyne receiver to minimize the power dissipation and system complexity. The direct-sampling digital radiometer uses a high-speed analog-to-digital converter and the principles of undersampling to perform direct detection of the signal. The analog-to-digital consists of a high-speed track-and-hold circuit (T/H) and digital comparator array.; This research presents the development of the analog-to-digital converter through design methodologies, simulation results, and analysis of key components. The development of a diode-bridge T/H circuit is presented. The circuit was optimized for low-power dissipation and fabricated using silicon germanium technology. The performance of the T/H demonstrated an average effective number of bits of 2.4 bits across several sampling frequencies at the measurement frequency for soil moisture. The total power dissipation of T/H circuit was 64 mW.