Design of a power-scaling, precision instrumentation amplifier using correlated double sampling

Abstract

With the ever increasing prevalence of battery powered electronics and the rise of the Internet of Things (IoT), power consumption has become a critical metric for electronic devices. In a sampling system, energy can be saved by power-cycling the electronics between the samples, only consuming significant power when a measurement needs to be taken. This strategy has limitations. With today's modern electronics, when the throughput of a signal chain drops below a certain threshold, the shutdown current starts to dominate the energy consumption of the system. This is not an efficient use of energy, and creates a "power-floor," where the signal chain can not operate below a minimum power. In other words, power consumption ceases to scale linearly with the throughput of the system. This thesis describes the design and operation of an amplifier that is intended to have low shutdown current and fast turn-on and turn-off times to minimize power consumed when not making a measurement. The proposed design is a switched capacitor circuit that uses an operational transconductance amplifier (OTA) to amplify a small differential signal produced by a sensor. The amplifier is intended to be used with the AD7686 successive approximation register (SAR) analog to digital converter (ADC) and a state-of-the-art voltage reference that has been created by Analog Devices Inc. (ADI) to efficiently power-cycle. Together, the amplifier, ADC, and voltage reference offer a complete signal chain that is capable of true power-cycling, and present a linear relationship between power consumption and sampling rate, particularly in low throughput domains, where prior technology has had difficulty doing so.