Wide-band low-input-impedance trans-impedance amplifiers for instrumentation applications

In this paper we investigate trans-impedance amplifiers which can be used to minimize the influence of stray capacitances on the operation of signal conditioners used for instrumentation applications such as inductive microsensors for micromachines. The effect of stray capacitances can be minimized when using this type of amplifier by ensuring that its input impedance is small. A technique for realizing very low input impedances over a wide bandwidth for these amplifiers is studied both analytically and experimentally for transistors having a wide range of gain-bandwidth products f(T). In addition an improved circuit configuration which further reduces the amplifier's input impedance at high frequencies is investigated by computer simulation.