低噪声无偏置电压-电流变换器

为解决电压-电流变换器电路的直流精度、噪声性能和交流性能间的矛盾,提出了一种直流部分与交流部分相对独立的电路结构.以两个对称的单晶体管共基组态放大器为交流变换单元,将交流输入电压变换为交流电流分量.一对匹配的精密恒流源电路分别为两个交流变换单元提供恒流偏置.将两个交流变换单元的输出电流叠加,抵消偏置电流,即可获得无偏置交流电流.该电路利用运放获得优异的直流性能,但运放位于交流回路之外.交流信号回路中只有晶体管和无源元件,从而同时实现了良好的噪声性能和高频性能.

Low-Noise Unbiased Voltage-Current Converter

To solve the comflicts between DC precision, noise performance and AC performance of traditional current-voltage converter, a noval circuit structure with seperated DC part and AC part was introduced. Two symmetric single transistor common-base amplifiers act as AC converting units and convert AC input voltage into AC components of output current. Two matched precision constant current sources provide constant bias current for AC converting units. By summing output current of both AC converting units and cancelling constant bias current, unbiased AC output current can be generated. This circuit achieves high DC precision by using op-amps, but op-amps are located outside AC loops. Since AC loops consist just transistors and inactive components, excellent noise performace and frequence performance can be realized at the same time.