Wideband Fully Differential Current Driver with Optimized Output Impedance for Bioimpedance Measurements

Abstract

This paper presents a wideband fully differential current driver architecture suitable for bioimpedance measurements. It uses an improved regulated cascode to enhance output impedance, enabling accurate measurements of transfer impedances at low and high frequencies. The current driver architecture maximizes the output voltage swing. An independent reference voltage is used in order to compensate the process variations of the output common mode voltage. The circuit was designed in 0.18µm CMOS AMS process, operating from 1.8V supply voltage. The silicon area is 0.26 mm 2. The current driver has a 67 MHz bandwidth and can provide a maximum output current of 600 µA peak to peak with a Total Harmonic Distortion (THD) below 0.3% at low frequencies increasing to 0.6% at 8 MHz. Due to the use of regulated cascodes in the output stage, the circuit achieves a 79MΩ output impedance at low frequencies decreasing to 324KΩ at 1MHz, with an output voltage swing of 0.95 V.

A Hybrid Bioimpedance Spectroscopy Architecture for a Wide Frequency Exploration of Tissue Electrical Properties

“…A. Topology Fig.2 shows the architecture of the current driver [5]. It is a symmetrical fully-differential Operational Transconductance Amplifier (OTA).…”

Design of current sources for load common mode optimization

“…Recently, Zhang et al developed a Mirrored Current Source using the IC AD844 (current-conveyor) to reduce analog common mode signals and digital common mode noise [ 19 ]. Due to low voltage power supply and relatively high current along with high interface electrode-interface impedance caused by effects like fibrosis, Lamlih et al developed an integrated differential current source to maximize the voltage output swing [ 20 ].…”