A Charge-Recycling Scheme and Ultra Low Voltage Self-Startup Charge Pump for Highly Energy Efficient Mixed Signal Systems-On-A-Chip

The advent of battery operated sensor-based electronic systems has provided a pressing need to design energy-efficient, ultra-low power integrated circuits as a means to improve the battery lifetime. This dissertation describes a scheme to lower the power requirement of a digital circuit through the use of charge-recycling and dynamic supply-voltage scaling techniques. The novel charge-recycling scheme proposed in this research demonstrates the feasibility of operating digital circuits using the charge scavenged from the leakage and dynamic load currents inherent to digital design. The proposed scheme efficiently gathers the “ground-bound” charge into storage capacitor banks. This reclaimed charge is then subsequently recycled to power the source digital circuit. The charge-recycling methodology has been implemented on a 12-bit Gray-code counter operating at frequencies of less than 50 MHz. The circuit has been designed in a 90-nm process and measurement results reveal more than 41% reduction in the average energy consumption of the counter. The total energy savings including the power consumed for the generation of control signals aggregates to an average of 23%. The proposed methodology can be applied to an existing digital path without any design change to the circuit but with only small loss to the performance. Potential applications of this scheme are described, specifically in wide-temperature dynamic power reduction and as a source for energy harvesters. The second part of this dissertation deals with the design and development of a self-starting, ultra-low voltage, switched-capacitor (SC) DC-DC converter that is essential to an energy harvesting system. The proposed charge-pump based SC-converter operates from 125-mV input and thus enables battery-less operation in ultra-low voltage energy harvesters. The charge pump does not require any external components or expensive post-fabrication processing to enable low-voltage operation. This design has been implemented in a 130-nm CMOS process. While the proposed charge pump provides significant efficiency enhancement in energy harvesters, it can also be incorporated within charge recycling systems to facilitate adaptable charge-recycling levels. In total, this dissertation provides key components needed for highly energy-efficient mixed signal systems-on-a-chip

Design and Analysis of a General Purpose Operational Amplifier for Extreme Temperature Operation

Operational amplifiers (op amps) are key functional blocks that are used in a variety of analog subsystems such as switched-capacitor filters, analog-to-digital converters, digital-to-analog converters, voltage references and regulators, etc. There has been a growing interest in using such circuits for extreme environment electronics, in particular for electronics capable of operating down to deep-cryogenic temperatures for lunar and Martian surface explorations. This thesis presents the design and analysis of a general purpose op amp suited for “extreme environment” applications, with a wide operating temperature range of 93 K to 398 K. The op amp has been implemented using a CMOS architecture to exploit the low temperature operational advantages offered by MOS devices, such as increase in carrier mobility, increased transconductance, and improved switching speeds. The op amp has a two-stage architecture to provide high gain and also incorporates common-mode feedback around the input stage. Tracking compensation has been implemented to provide stable frequency compensation over wide temperature. The op amp has been fabricated in a commercial 0.35-μm 3.3-V SiGe BiCMOS process. The op amp has been tested for the temperature range of 93 K to 398 K and is unity-gain stable and fully functional over this range. This thesis begins with a study of the impact of temperature on MOS devices and operational amplifiers. Next, the design of the wide temperature general-purpose operational amplifier is presented along with an analysis of the common-mode feedback circuit. The op amp is then characterized using simulation results. Finally, the test setup is presented and the measurement results are compared with those from simulation

A SiGe BiCMOS Instrumentation Channel for Extreme Environment Applications

An instrumentation channel is designed, implemented, and tested in a 0.5-μm SiGe BiCMOS process. The circuit features a reconfigurable Wheatstone bridge network that interfaces an assortment of external sensors to signal processing circuits. Also, analog sampling is implemented in the channel using a flying capacitor configuration. The analog samples are digitized by a low-power multichannel A/D converter. Measurement results show that the instrumentation channel supports input signals up to 200 Hz and operates across a wide temperature range of -180°C to 125°C. This work demonstrates the use of a commercially available first generation SiGe BiCMOS process in designing circuits suitable for extreme environment applications