Title :
Biocompatible, High Precision, Wideband, Improved Howland Current Source With Lead-Lag Compensation
Author :
Tucker, A.S. ; Fox, R.M. ; Sadleir, Rosalind J.
Author_Institution :
J. Crayton Pruitt Family Dept. of Biomed. Eng., Univ. of Florida, Gainesville, FL, USA
Abstract :
The Howland current pump is a popular bioelectrical circuit, useful for delivering precise electrical currents. In applications requiring high precision delivery of alternating current to biological loads, the output impedance of the Howland is a critical figure of merit that limits the precision of the delivered current when the load changes. We explain the minimum operational amplifier requirements to meet a target precision over a wide bandwidth. We also discuss effective compensation strategies for achieving stability without sacrificing high frequency output impedance. A current source suitable for Electrical Impedance Tomography (EIT) was simulated using a SPICE model, and built to verify stable operation. This current source design had stable output impedance of 3.3 MΩ up to 200 kHz, which provides 80 dB precision for our EIT application. We conclude by noting the difficulty in measuring the output impedance, and advise verifying the plausibility of measurements against theoretical limitations.
Keywords :
SPICE; bioelectric phenomena; biomedical electronics; charge pump circuits; circuit stability; constant current sources; electric impedance imaging; operational amplifiers; Howland current pump; SPICE model; alternating current; biocompatibility; bioelectrical circuit; biological loads; compensation strategies; current source; current source design; electrical currents; electrical impedance tomography; high frequency output impedance; high precision delivery; improved Howland current source; lead-lag compensation; operational amplifier; output impedance; plausibility measurements; resistance 3.3 Mohm; target precision; wide bandwidth; Bandwidth; Circuit stability; Impedance; Lead; Noise; Resistors; Tomography; Bioimpedance; Howland current source; electrical impedance tomography (EIT); electrical stimulation; Dielectric Spectroscopy; Electric Impedance; Models, Theoretical; Tomography;
Journal_Title :
Biomedical Circuits and Systems, IEEE Transactions on
DOI :
10.1109/TBCAS.2012.2199114
