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Howland current source for high impedance load applications.

K F Morcelles¹, V G Sirtoli¹, P Bertemes-Filho¹

¹Department of Electrical Engineering, Santa Catarina State University, Joinville 89.219-710, Brazil.

The Review of Scientific Instruments

|December 3, 2017

Summary

This summary is machine-generated.

The Load-in-the-Loop Compensated Enhanced Howland Source (LLC-EHCS) significantly improves accuracy for Electrical Impedance Spectroscopy (EIS) applications. This novel circuit design minimizes output current errors at high frequencies and high load impedances, expanding EIS capabilities.

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Area of Science:

Electrical Engineering
Biomedical Instrumentation
Signal Processing

Background:

The Enhanced Howland Current Source (EHCS) is widely used for Electrical Impedance Spectroscopy (EIS) excitation due to its simplicity and reliability.
Standard EHCS circuits suffer from output impedance degradation at high frequencies, limiting their use in high load impedance applications like those using dry or microelectrodes.

Purpose of the Study:

To design and validate a modified EHCS circuit that overcomes high-frequency output impedance limitations.
To enhance the performance of excitation circuits for high load impedance and wide bandwidth EIS applications.

Main Methods:

A mathematical model was developed to guide the design of a new EHCS circuit incorporating an output current buffer and frequency compensation.
The proposed Load-in-the-Loop Compensated Enhanced Howland Source (LLC-EHCS) was simulated using PSpice for proof of concept.
Experimental measurements were conducted to compare the performance of the LLC-EHCS against the standard EHCS.

Main Results:

The LLC-EHCS demonstrated output current errors below 1% up to 3.7 MHz for load impedances between 560-2200 Ω, and up to 1.2 MHz for a 5.6 kΩ load.
In contrast, the standard EHCS exhibited errors exceeding acceptable limits at much lower frequencies (170 kHz and 80 kHz, respectively).
The LLC-EHCS also achieved a 3x higher output linear swing compared to the standard EHCS.

Conclusions:

The proposed LLC-EHCS effectively addresses the high-frequency limitations of standard EHCS circuits.
The LLC-EHCS is a suitable excitation circuit for demanding high load and wide bandwidth Electrical Impedance Spectroscopy applications.
This advancement enables more accurate and reliable EIS measurements in challenging electrode configurations.