面向生物阻抗测量的双通道反馈电流源设计

Design of dual-channel feedback current source for bio-impedance measurement

微电流激励的生物阻抗测量方法在生物医学中具有广泛应用前景,其中能够驱动生物负载的电压控制电流源是生物阻抗测量的前提条件。本文提出一种具有高带宽、高输出阻抗、能驱动较大容性负载的电流源电路拓扑结构。首先,根据系统的传递函数分析系统不稳定的原因并引入容性负载对系统的影响;接着,使用双通道反馈补偿的方法弥补了系统高频不稳定的缺陷,并在反馈通路使用简单的阻容网络实现容性负载的补偿;然后,仿真分析得出电流源在100 Hz^1.2 MHz的带宽范围内具有较好的恒流特性,在1 MHz的输出阻抗达到为160.756 kΩ,并且当负载的复阻抗越大时,系统稳定裕度越高。最后,使用该电流源激励生物组织进行实验验证,在不同的频率下对比传统增强型Howland和三运放电流源,结果表明在800 KHz以上,其它两种电流源无法成像时该电流源仍具有很好的成像效果,也验证了该电流源在测量生物组织时的实用性。

The micro-current-excited bio-impedance measurement method has been widely applied in the biomedicine.The voltage-controlled current source that is capable of driving the bio-load is a prerequisite for the bio-impedance measurement.In this study,a current source circuit topology with the high bandwidth,high output impedance and large driving capacitive load is proposed.First,the cause of the system instability is analyzed based on the transfer function of the system.The influences of the capacitive load on the system are introduced.Secondly,the two-channel feedback compensation method is used to make up for the high-frequency instability of the system.The simple resistance-capacitance network is used in the feedback path to achieve compensation of the capacitive load.Thirdly,simulation analysis shows that the current source has good constant current characteristics in the bandwidth range of 100 Hz^1.2 MHz.The output impedance at 1 MHz is 160.756 kΩ.When the complex impedance driving the load is larger,the system stability margin is higher.Finally,the current source is utilized to stimulate biological tissues for experiment evaluation.The traditional enhanced Howland and three op amp current sources are compared at different frequencies.Results show that the other two current sources cannot be imaged when the frequency is above 800 KHz.In contrast,the current source has a good imaging effect,which verifies the practicality of the current source when measuring biological tissues.