Wide-Bandwidth Electronically Programmable CMOS Instrumentation Amplifier for Bioimpedance Spectroscopy

Abstract

An instrumentation amplifier (IA) with continuous tuning of the voltage gain, suitable for operation over a wide frequency range, and aimed to electrical bioimpedance spectroscopy, is proposed. The operation principle of the IA is based on indirect current feedback (ICF), which leads to an almost-constant bandwidth regardless of the value of the programmed voltage gain. The use of improved voltage followers in the transconductors required in the ICF technique allows achieving a compact implementation with a bandwidth compatible with bioimpedance spectroscopy applications. The tuning strategy relies on a continuously programmable current mirror that can be electronically adjusted by means of a control current. The IA has been designed and fabricated in 180 nm CMOS technology to operate with a 1.8-V single supply. The experimental characterization of the silicon prototypes showed a gain programmability range higher than 45 dB, between −4.6 dB and 41.2 dB, a BW around 3 MHz, and a maximum CMRR at DC higher than 86 dB, all this with a minimum current consumption of $144.8~\mu \text{A}$ and an area occupation of 0.0196 mm2.

Keywords

• Bioimpedance spectroscopy
• electronic tuning
• indirect current feedback
• instrumentation amplifier
• wide bandwidth