The Howland current source(HCS)circuit is commonly used,e.g.in electrical impedance tomography(EIT)systems.It is important to optimise the design parameters,such as the output impedance,bandwidth,current stability and...The Howland current source(HCS)circuit is commonly used,e.g.in electrical impedance tomography(EIT)systems.It is important to optimise the design parameters,such as the output impedance,bandwidth,current stability and load range.While many people have used this circuit,it has not been systematically analysed.In this paper,a numerical method is proposed to analyse the characteristics of HCS.Based on a non-ideal op-amp model,general formulas and simplified formulas for calculating the output impedance and the close-loop gain of HCS are deduced.From these formulas,the practical formulas are chosen and their effectiveness has been proven by analysis and experiment.The output impendence of two HCS circuits based on μA741 and LM6365 are compared.The magnitude-frequency response and the relationship between the current and the load of HCS are discussed.展开更多
针对传统Howland电流源电路受输出负载影响,稳定性差、控制精度低以及分辨率低的问题,以TMS570为控制核心,设计上位机软件控制12 bits数模转换器(Digital to Analog Converter,DAC)产生电压基准,实时控制改进型Howland电流源电路。同时...针对传统Howland电流源电路受输出负载影响,稳定性差、控制精度低以及分辨率低的问题,以TMS570为控制核心,设计上位机软件控制12 bits数模转换器(Digital to Analog Converter,DAC)产生电压基准,实时控制改进型Howland电流源电路。同时通过软硬件实时采样、比较,精确控制、补偿、反馈电流值,提高了整个电路的安全性和准确性。测试结果表明,该电流源输出不受负载影响,安全性、电流精度以及分辨率适用于力矩电机等高精度和高安全性要求,并且易于扩展升级。展开更多
设计了一种基于电流模电路的宽带电流放大器。系统由宽带I/V变换器、电压放大器以及宽带压控电流源三模块直接耦合级联而成。详细论述了电路设计原理、电路结构以及元件参数选择方法。通过选用电流反馈型运算放大器设计电路,不受电压反...设计了一种基于电流模电路的宽带电流放大器。系统由宽带I/V变换器、电压放大器以及宽带压控电流源三模块直接耦合级联而成。详细论述了电路设计原理、电路结构以及元件参数选择方法。通过选用电流反馈型运算放大器设计电路,不受电压反馈型运放增益带宽积和有限压摆率的限制,提高了电流放大器的带宽;用负载接地的豪兰德电流源设计压控电流源,实现较高精度的V/I转换;采用三级结构,增益及带载能力可以根据实际需要灵活调节。系统仿真结果表明,论述的电路设计方法是可行的。测得典型电路的输入电阻约为0.13Ω,输出电阻为约59 kΩ,电流增益为60 d B。展开更多
文摘The Howland current source(HCS)circuit is commonly used,e.g.in electrical impedance tomography(EIT)systems.It is important to optimise the design parameters,such as the output impedance,bandwidth,current stability and load range.While many people have used this circuit,it has not been systematically analysed.In this paper,a numerical method is proposed to analyse the characteristics of HCS.Based on a non-ideal op-amp model,general formulas and simplified formulas for calculating the output impedance and the close-loop gain of HCS are deduced.From these formulas,the practical formulas are chosen and their effectiveness has been proven by analysis and experiment.The output impendence of two HCS circuits based on μA741 and LM6365 are compared.The magnitude-frequency response and the relationship between the current and the load of HCS are discussed.
文摘针对传统Howland电流源电路受输出负载影响,稳定性差、控制精度低以及分辨率低的问题,以TMS570为控制核心,设计上位机软件控制12 bits数模转换器(Digital to Analog Converter,DAC)产生电压基准,实时控制改进型Howland电流源电路。同时通过软硬件实时采样、比较,精确控制、补偿、反馈电流值,提高了整个电路的安全性和准确性。测试结果表明,该电流源输出不受负载影响,安全性、电流精度以及分辨率适用于力矩电机等高精度和高安全性要求,并且易于扩展升级。
文摘设计了一种基于电流模电路的宽带电流放大器。系统由宽带I/V变换器、电压放大器以及宽带压控电流源三模块直接耦合级联而成。详细论述了电路设计原理、电路结构以及元件参数选择方法。通过选用电流反馈型运算放大器设计电路,不受电压反馈型运放增益带宽积和有限压摆率的限制,提高了电流放大器的带宽;用负载接地的豪兰德电流源设计压控电流源,实现较高精度的V/I转换;采用三级结构,增益及带载能力可以根据实际需要灵活调节。系统仿真结果表明,论述的电路设计方法是可行的。测得典型电路的输入电阻约为0.13Ω,输出电阻为约59 kΩ,电流增益为60 d B。
