Electronic Military & Defense Annual Resource

6th Edition

Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.

Issue link: https://electronicsmilitarydefense.epubxp.com/i/707574

Contents of this Issue

Navigation

Page 15 of 43

Techniques Selecting A Low-Voltage Multiplexer For Signal Processing Satellite Telemetry Military communications can be a matter of life and death, making proper component choices for military satellites crucial. By Kiran Bernard and Joshua Broline P er the Union of Concerned Scientists, 1,381 satellites orbited Earth as of January 2016. Of those, 568 belonged to the United States or United States- based companies and contractors. Of those, 149 are identified as military satellites, and each one has been launched with a purpose, be it reconnaissance and surveillance, signals intelligence, meteorology, navigation, or communications. Communication satellites feature a plethora of sensors that read out various telemetry test points and statuses for mission-critical systems. Because digital microprocessors have a limited number of input/output (I/O) pins, they interface with these sensors using multichannel analog multiplexers, which then continuously process and output the hundreds of telemetry signals into an analog-to-digital converter's (ADC) input. Satellite telemetry systems rely on these key components to achieve mission assurance for long-duration space flights. Analog multiplexers are a staple for this critical signal processing application. Multiplexers take up only one I/O pin for reading sensors and are limited only by the number of available input channels (Figure 1). Following the semiconductor industry trend, power voltage rails have fallen, and thus the need for a low-voltage multiplexer that can work in radiation-prone environments has emerged. This article discusses the challenges of using low voltage 5V analog multiplexers for satellite applications that must withstand the effects of radiation exposure and single-event effects (SEE). We'll also examine the trade-offs of switch on-resistance, switch input leakage, and propagation delays, including their impact on power consumption and system performance. Examining Multiplexer Trade-offs There are options currently available to fulfill the satellite industry's analog multiplexer needs, but none is a particularly ideal solution. One available option is to use a high-voltage multiplexer because its input range would more than encompass the needs of a low-voltage sensor, but this option would require a negative power supply rail just for the multiplexer. This option is, in fact, being used in many low-voltage applications today, but the extra negative voltage rail is undesirable. The other option is to get a multiplexer that's meant to work at lower voltages. There are 5V options, but almost all of them make the satellite design engineer choose between lower switch on-resistance and lower switch input leakage. This choice is a trade-off every engineer has to make: when the switch is on, the on-resistance distorts the input signal, and, while the switch is off, the switch's leakage provides a constant drain on the batteries. Choosing one or the other is a choice between getting more precise sensor readings or getting longer battery life, both of which are critical to satellites. As with other lower-voltage devices, propagation delays get smaller, so having a multiplexer that can keep up is an advantage. High-voltage multiplexer options generally have much longer delays because of the larger devices they use. Faster address transition times translate to getting data closer to real-time, and this is key, because the reaction of backup or countermeasure systems can occur much faster when sensors report a critical condition. Handling Radiation Exposure However, just being fast is not good enough. In space, integrated circuits (ICs) are exposed to radiation in ways that can prevent them from working in full order. Having Electronic Military & Defense Annual Resource, 6th Edition 16 Figure 1: 16-channel multiplexer; typical application diagram

Articles in this issue

Archives of this issue

view archives of Electronic Military & Defense Annual Resource - 6th Edition