Grando Sirtoli Vinicius, Coelho Vincence Volney, Bertemes-Filho Pedro
Univeridade do Estado de Santa Catarina (UDESC), Rua Paulo Malschitzki, 200, Campus Universitario Prof. Avelino Marcante, Bairro Zona Industrial Norte, Joinville, SC, Brazil.
Rev Sci Instrum. 2019 Feb;90(2):024702. doi: 10.1063/1.5079872.
An impedance spectrum is calculated by the ratio between an injecting current and a resulting measured voltage, which allows the extraction of electrical properties from the material under study. The current source is considered an essential block to deliver a controlled current to a wide range of working loads and large bandwidth. To comply with such requirements, the current source output impedance must be much higher than the load impedance at each discrete frequency within the range. However, stray capacitance from cables and circuitry reduce the output impedance, especially at higher frequencies. We proposed a modified mirrored enhanced Howland current source (MEHCS) by using the feedback technique for a wide frequency range applications on electrical bioimpedance. We implemented four MEHCS circuits [with/without multiplexer (MUX) and with/without feedback], and then the output current and impedance were measured up to 20 MHz. The proposed current source showed an improvement in the frequency response at lower and higher frequencies when compared to the standard circuit. The measured output impedance was 10 times higher in the proposed circuit than in the standard MEHCS. The use of a feedback also increased the bandwidth in almost one decade in low and high frequencies when loaded with a resistor of about 1 kΩ.
通过注入电流与所测电压之比计算阻抗谱，这使得能够从被研究材料中提取电学特性。电流源被视为一个关键模块，用于向广泛的工作负载和大带宽提供受控电流。为满足此类要求，在该范围内的每个离散频率处，电流源输出阻抗必须远高于负载阻抗。然而，电缆和电路中的杂散电容会降低输出阻抗，尤其是在较高频率时。我们提出了一种改进的镜像增强型霍兰德电流源（MEHCS），通过使用反馈技术用于电生物阻抗的宽频率范围应用。我们实现了四个MEHCS电路[带/不带复用器（MUX）以及带/不带反馈]，然后测量了高达20 MHz的输出电流和阻抗。与标准电路相比，所提出的电流源在低频和高频时的频率响应都有改善。在所提出的电路中，测得的输出阻抗比标准MEHCS高10倍。当加载约1 kΩ的电阻时，反馈的使用在低频和高频时也使带宽增加了近一个数量级。
