A High Quality Controlled Current Source

A technique for realizing a high-quality controlled current source is described. A monolithic operational amplifier is used as the main building block, and a modified current mirror is used to recover the signal current from the power supply leads of the amplifier. The proposed mirror exhibits low input resistance, which reduces errors due to the noninfinite power-supply rejection characteristics of the amplifier, and a current-splitting network allows the realization of output impedances in the range of tens of megohms using standard components. The entire circuit operates in a class-AB mode for high drive capability with low values of quiescent current. A simple application is included to show that a voltage amplifier can readily be constructed which exhibits a 3-dB gain-bandwidth product forty times larger than the gain-bandwidth product of the operational amplifier used. Detailed experimental results are included to verify predicted frequency response and gain characteristics.