Comparative study of voltage controlled current sources for biompedance measurements

For bioimpedance measurement, the design of a voltage controlled current source (VCCS) is important to have a good compromise between performance of final results and patient safety. VCCS should have simultaneously large output impedance and wide bandwidth. In this paper, we compare between the Tietze topology, with and without Negative Capacitance Circuit (NCC), and the Improved Howland Current pump ICSA topology. Best results were reached with a Tietze current source with NCC over a wideband frequency range from 10 KHz to 1 MHz. The experiments show that the Tietze VCCS is able to drive loads of 25 Ω to 10 KΩ with current amplitude below 0.5 mA within the accuracy of 0.57% in practice. This fulfills even the requirements for bioimpedance measurements especially at high frequency and high load impedance.