Chen D X, Deng X, Yang W Q
School of Mechatronics Engineering and Automation, National University of Defense Technology, Changsha 410073, China.
Rev Sci Instrum. 2010 Mar;81(3):034704. doi: 10.1063/1.3367879.
The capacitance of a single electrode is usually measured by injecting a current to the electrode and measuring the resultant voltage on the electrode. In this case, a voltage-controlled current source with a high bandwidth is needed because the impedance is inversely proportional to the excitation frequency. In this design note, three different current sources are discussed: (1) the Howland current source, (2) a modified Howland current source, and (3) a dual op-amp current source. The principle and dynamic performances are presented and compared. Simulation and experimental results show that although the Howland current source has the lowest (i.e., worst) output impedance, its output is the most stable among the three current sources when the frequency changes. Therefore, it is suitable for single-electrode capacitance measurement. Initial tests have proven the feasibility of single-electrode capacitance sensor with the Howland current source.
单个电极的电容通常通过向电极注入电流并测量电极上产生的电压来测量。在这种情况下，需要一个具有高带宽的压控电流源，因为阻抗与激励频率成反比。在本设计笔记中，讨论了三种不同的电流源：(1) 霍兰德电流源，(2) 改进的霍兰德电流源，以及 (3) 双运算放大器电流源。介绍并比较了它们的原理和动态性能。仿真和实验结果表明，虽然霍兰德电流源的输出阻抗最低（即最差），但在频率变化时，其输出在三种电流源中是最稳定的。因此，它适用于单电极电容测量。初步测试已经证明了采用霍兰德电流源的单电极电容传感器的可行性。
