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Published on: March 19, 2016
A comparison of modified Howland circuits as current generators with current mirror type circuits
P Bertemes-Filho1, B H Brown, A J Wilson
1Department of Medical Physics and Clinical Engineering, Royal Hallamshire Hospital, University of Sheffield, UK. mpp98pb@sheffield.ac.uk
Physiological Measurement
|March 17, 2000
Summary
Two current generator circuits for multi-frequency electrical impedance tomography (EIT) were compared. Both modified Howland and current mirror circuits showed stability and minimal current variation, making them suitable for practical EIT applications.
Area of Science:
- Biomedical Engineering
- Electrical Engineering
- Medical Imaging
Background:
- Multi-frequency electrical impedance tomography (EIT) demands stable voltage-controlled current generators.
- These generators must operate across a wide frequency range and accommodate varying load impedances.
Purpose of the Study:
- To compare the performance of a modified Howland circuit and a current mirror circuit for EIT applications.
- To evaluate their stability, output current variation, and output impedance over a broad frequency range.
Main Methods:
- Utilized PSPICE simulations and physical measurements to assess circuit performance.
- Tested both modified Howland and current mirror circuits from 1 kHz to 1 MHz.
- Measured output current and output impedance characteristics.
Main Results:
- Both circuits demonstrated stability between 1 kHz and 1 MHz.
- Maximum output current variation was 2.0% for the Howland circuit and 1.6% for the current mirror circuit.
- Both achieved >100 kohms output impedance up to 100 kHz, but not at 1 MHz.
Conclusions:
- The modified Howland and current mirror circuits are comparable for practical EIT implementation.
- Both designs offer stable performance suitable for multi-frequency EIT systems.
- Minor differences in current variation and output impedance do not significantly favor one over the other for general use.
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