用于生物电阻抗谱测量的程控宽频恒流源设计

Design of programmable broadband constant current source applied to bioelectrical impedance measurement

恒流源作为生物电阻抗谱测量系统中的激励信号,需要输出频带宽、电流稳定。为此,提出了一种程控宽频恒流源设计方案,以STM32单片机为控制核心,通过DDS数字信号发生器产生频率可调的正弦电压信号,经Tietze电流泵进行电压电流转换,转换频带宽,畸变小的电流信号,利用以MCP41010数字电位器为调节单元的程控增益放大,解决恒流源的高频衰减问题。在仿真实验证明恒流源随频率和负载改变输出特性优良的基础上,研制了恒流源装置。实验表明,恒流源可控输出频率为0~1 MHz,负载能力为0~5.4 kΩ,电流有效值随频率、负载改变平均误差分别为0.137%、0.251%,具有输出频带宽、带负载能力强、电流输出稳定特点,能够满足生物电阻抗谱测量需求。

As the excitation signal in the bioelectrical impedance measurement system,the constant current source needs to output a wide frequency band and stable current.In this paper,a program-controlled broadband constant current source design scheme is proposed:With STM32 as the control core,sinusoidal voltage signal with adjustable frequency is generated though the DDS.Tietze current pump a current conversion is performed with wide frequency bandwidth and small distortion.By the MCP41010 digital potentiometer,a numerical control gain amplifier circuit is designed to solve the problem of high frequency attenuation of constant current source.Based on the simulation experiment proved that the constant current source has excellent output characteristics with frequency and load changes,the constant current source transposition was developed.Experimental data shows that the controllable output frequency range is 0~1 MHz,the load capacity range is 0~5.4 kΩ.The average error of the current effective value changes with frequency and load is 0.137%and 0.251%respectively.Proved that it has the characteristics of wide output frequency band,strong load capacity and stable current output which can meet the needs of bioelectrical impedance spectrum measurement.