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Related Experiment Video

Updated: Feb 17, 2026

Impedance Pneumography for Minimally Invasive Measurement of Heart Rate in Late Stage Invertebrates
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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
PubMed
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.