Wide-temperature and extreme-environment electronics are crucial to future missions. These missions will not have the weight and power budget for heavy harnesses and large, inefficient warm boxes. In addition, extreme-environment electronics, by their inherent nature, allow operation next to sensors in the ambient environment, reducing noise and improving precision over the warm-box-based systems employed today.
Current sensing applications are key in motor and power supply control applications. As higher levels of integration in spacecraft systems are sought, it is desired to integrate high-voltage interfaces onto highly integrated “System-on-Chip” (SoC) components utilizing low-voltage CMOS (complementary metal–oxide–semiconductor) process technology.
A circuit for a capacitively coupled, level-shifting, high-voltage current sense for extreme environments is disclosed. This circuit uses custom, on-chip, high-voltage components using standard CMOS masks to enable a high-voltage switched-capacitor differencing amplifier. Low-temperature-coefficient components and temperature-compensated biasing enable extreme-environment operation. The ability to integrate this type of component into large-scale, mixed-signal systems is a crucial advantage.
Extreme-environment electronics are valuable to a number of disciplines, including military/aerospace, automotive, scientific research applications, and energy.
This work was done by Jeremy A. Yager, Mohammad M. Mojarradi, Bruce R. Hancock, and Tuan A. Vo of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48542
This Brief includes a Technical Support Package (TSP).
Capacitively Coupled, High-Voltage Current Sensing for Extreme Environments
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Overview
The document titled "Capacitively Coupled, High-Voltage Current Sensing for Extreme Environments" presents research conducted by the Jet Propulsion Laboratory (JPL) at the California Institute of Technology, focusing on the development of a high-voltage current sensing circuit suitable for extreme environments, such as those encountered in space applications.
The primary objective of this research is to enhance current sensing capabilities in motor and power supply control systems by integrating high-voltage interfaces into highly integrated 'System-on-Chip' (SoC) components using low-voltage CMOS process technology. This integration is crucial as spacecraft systems increasingly demand higher levels of integration while maintaining reliability under extreme conditions.
The document describes a capacitively coupled high-voltage current sensing circuit that operates using two non-overlapping clock phases, φ_ZERO and φ_READ. During φ_ZERO, a voltage difference is established across a high-voltage capacitor, while φ_READ connects the capacitor to the input voltage, resulting in a tenfold gain of the differential voltage. The design includes a differential version of the circuit to enhance performance.
To ensure high-voltage operation, the circuit employs a high-voltage N-well structure, which is developed using standard in-process masks, eliminating the need for custom processing. The design also incorporates protection diodes to safeguard the PMOS transistors from out-of-compliance voltages, as well as a high-voltage capacitor cell designed for a breakdown voltage of approximately 100 V.
The document highlights the importance of extreme temperature range operation, achieved through various design techniques, including constant-gm current biasing and Minch cascode biasing. These methods, along with the use of metal-fringing and MIM capacitors, help maintain circuit performance across a wide temperature range.
Additionally, the circuit design includes off-chip current sense resistors, which are standard practice in power systems due to the high currents involved, exceeding the capabilities of integrated circuits. The use of 30 kΩ resistors on-chip serves to isolate PMOS switch transistors from transients, further enhancing the circuit's robustness.
Overall, this research represents a significant advancement in the field of high-voltage current sensing, providing a reliable solution for extreme environment applications, particularly in aerospace and spacecraft systems. The findings are part of NASA's broader efforts to develop technologies with potential commercial applications.
