Although the integrated current source has an output impedance greater than 1 MOmega up to 1 MHz in simulations, in practice, the impedance is greater than 160 kOmega up to 1 MHz due to the presence of stray capacitance. For frequencies up to 1 MHz, the measured maximum variation of the output current for the integrated current source is 0.8% whereas for the MHC the corresponding value is 1.5%.

The output current and the output impedance of both circuits were determined through simulations and measurements over the frequency range of 10 kHz to 1 MHz. The new integrated design has advantages over the MHC in terms of power consumption and area. In this paper, we introduce a new integrated current source design in CMOS technology and compare its performance with the MHC. The MHC requires tight matching of resistors to achieve high output impedance and may suffer from instability over a wide frequency range in an integrated solution. The most commonly employed current source design in EIT systems is the modified Howland circuit (MHC). Multi-frequency electrical impedance tomography (MF-EIT) systems require current sources that are accurate over a wide frequency range (1 MHz) and with large load impedance variations. Hong, Hongwei Rahal, Mohamad Demosthenous, Andreas Bayford, Richard H Note: Temperature effects in the modified Howland current source for electrical bioimpedance spectroscopyĬomparison of a new integrated current source with the modified Howland circuit for EIT applications. Operational amplifiers with a low temperature drift and matching resistor should be carefully considered in order to prevent oscillations at high temperatures. It was showed that the MHCS is stable at temperatures below 70 ☌. The measurements were made inside a temperature controlled environment. Parameters like output current, output impedance, total harmonic distortion, and oscillation have been measured.

The source has been tested in a temperature range from 20 to 70 ☌ and frequency range from 100 Hz to 1 MHz. The aim of this study is to show how the modified Howland current source (MHCS) is affected by temperature changes. Note: Temperature effects in the modified Howland current source for electrical bioimpedance spectroscopy.

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