Analysis and Design of Noise-Scalable Energy-Efficient Instrumentation Amplifier

Sensors are everywhere nowadays. They build a connection between the physical world and the electrical world. Almost all physical quantities can be captured by sensors and converted into electrical quantities. For precision sensor readout, instrumentation amplifier (IA) is a critical circuit block. Notably, for Internet of things (IoT) applications, IAs used in the sensing nodes should be low-cost and energy-efficient. In IA design, chopper stabilization technique is often used to suppress low-frequency disturbances by modulating them to higher frequencies. However, it introduces a ripple to the IA output and reduces the usable output swing, especially in deep sub-micron processes with limited voltage headroom. For the first time, this research analyzed the output ripple shape and amplitude of a capacitively-coupled instrumentation amplifier (CCIA). It finds that the output ripple relies on five design parameters and appears in four different forms. These findings are verified by silicon results and serve as a general guideline to design practical chopper-based amplifiers and corresponding ripple reduction techniques. In this research, we also proposed a power-up calibration scheme to mitigate the offset of a CCIA. In this design, the first stage of the amplifier is formed by multiple identical slices. During calibration, each slice's offset polarity is determined by reusing the amplifier's second stage as a comparator. With the polarity information, the first stage is regrouped to achieve a statistical offset reduction. The proposed amplifier has been fabricated in a standard 0.18 μm CMOS process with an area of 0.57 mm², achieving an average peak-to-peak output ripple of 58 mV. Compared to the state-of-the-art designs, the proposed scheme's calibration time is much shorter (14 clock cycles), and the overhead logic consumes zero static power after calibration. The total power consumption of this IA is 1.53 μW with a 1.2 V supply. Also, the proposed slicing technique provides an extra degree of freedom to the amplifier for bandwidth- and noise-scaling.