Low Power Embedded Control Design

This paper describes laboratory design exercises to introduce the added constraints of low power consumption to microcontroller design. Many new hand-held, portable, and remote instruments must operate several years on small, commercially available batteries. This means reducing the average consumption to less than 100 microamps. In add ition, the system hardware and software architecture must be interrupt-driven. Also, reduced noise margins, varying supply voltage, increased power supply impedance, burst-mode analog signal conditioning, and serial communications all present unique problems to the designer. Most modern high performance microcontrollers and microcomputers include software selectable modes of power reduction. This is often done by manipulating the on-board oscillator and providing an external wake-up interrupt. These modes can be used to reduce the typical 10-100 m illia p current consumption down three orders of magnitude. Also, recent high efficiency power supply regulators now include very low dropout voltage, low quiescent currents, power shut down control, and large input voltage range. A wide variety of these regulators are available in both linear and switchmode. Some provide extra features such as low battery voltage detector and indication. Some new high precision analog to digital converters require low power supply current during normal operation, and can be shut down to consume extremely low power when not in use. They require a minimum amount of setup time and are easily interfaced to the microcontroller via fast standard serial data communication. Internal auto-calibration permits full offset and span correction by the microcontroller. Additional features may include multiple channels, differential inputs, noise rejection, reduced parts count, and medium speed conversions. These emerging technologies are incorporated in laboratory design exercises, and presented as part of an intermediate level microprocessor course in the Electrical Engineering Technology program at Penn State Erie.