Comparative Study of Howland Current Source Configurations for Accurate Biomedical Devices

Embedded bioimpedance devices are in high demand for the improvement of the healthcare systems. These devices require an accurate and stable current source with a high output impedance in the frequency range from 5 kHz to 1 MHz for a load range from 100 Ω to 10 kΩ. The output impedance should be higher than 10 MΩ at 5kHz and 1 MΩ at 1 MHz. In this paper, a comparison between the inverting single configuration and the inverting dual configuration of the Howland current source is discussed. For the evaluation of the circuit performances, two parameters are considered: resistor configurations and amplifier characteristics. The results shows that the inverting dual configuration using the operational amplifier AD8021 with a very high bandwidth has the highest output impedance values (higher than 1 MΩ at 1 MHz).