基于数字相敏检波的恒流源输出阻抗检测及补偿技术实现

Method for Impedance Detection and Compensation Technique Based on DPSD

目的:为了提高电阻抗成像系统(EIT)的图像重构精度,研究并实现了恒流源输出阻抗值的检测以及补偿技术。方法:在EIT系统上设计了恒流源输出阻抗检测电路,用高速AD采回检测电路的输出电压值,并在数字信号处理器(DSP)实现数字相敏检波(DPSD)后得到恒流源输出阻抗。之后在恒流源输出端并联负电容补偿恒流源输出电容,以增大恒流源输出阻抗,提高EIT系统图像重构精度。结果:由实验结果发现,负电容补偿技术虽然无法使恒流源输出阻抗值趋于无穷,但是可使其阻抗值明显增大。结论:该阻抗检测方法及补偿电路独立于恒流源设计,是恒流源设计之外的测量和进一步提高其输出阻抗的方法,不仅可以很好地应用于EIT系统,也可以应用于其他对恒流源输出阻抗有较高要求的系统。

Objective To improve the precision of image reconstruction in electrical impedance tomography（EIT）,this pa-per discusses and realizes the method of impedance detection and its compensation technique.Methods It designed the impedance detection circuit in EIT,used high speed AD to collect the output voltage of impedance detection circuit.The digital signal processor（DSP） used these voltage values to obtain the output impedance based on digital phase sensitivity detection（DPSD）.Then it designed negative capacitance circuit in parallel with constant current source to improve the impedance. Results The result of experiments shows that： although the negative capacitance compensation technique can＇t let the output impedance approach to infinite, it can improve it obviously. Conclusion The method of impedance detection and its compensation technique are independent of constant current source. They can be not only applied to EIT but also used in other system whose constant current source needs high output impedance.