Stability and noise performance of constant transimpedance amplifier with inductive source

The design of a low-noise wideband transimpedance amplifier which matches an inductive source is considered. The presence of an inductive source makes it difficult to design such an amplifier to meet both low-noise and stability requirements. A novel feedback configuration is proposed. The use of this configuration gives good noise performance and at the same time realizes a constant transimpedance. The stability and signal transfer conditions for four different cases are derived. Noise analysis and optimization performed for each case yield amplifiers with optimal noise performance. Four amplifiers have been designed to verify the analytical results. The amplifier is suitable to be implemented in bipolar junction transistor technology and can be used as the preamplifier in an upconversion radio receiver. A transimpedance of 220 k Omega and total equivalent input noise current density between 0.35 to 0.75 pA/ square root Hz have been achieved in the whole AM band. A reduction of two in noise current has been measured when a JFET (junction field-effect-transistor) is used as input instead of a bipolar transistor.>