Application of transformer for improvement of noise performance of ultrasonic preamplifier

Abstract

The paper is analyzing the transformer application in the preamplifier input stages with aim to improve the noise performance. Transformer models used incorporate the winding losses for case with low transducer output impedance. In case of high transducer output impedance transformer core losses are taken into account. Core losses are encountered using shunt resistance R_c. Assuming that ultrasonic transducer impedance can not be modified it makes sense to use the noise figure instead of signal-to-noise ratio for the preamplifier noise performance analysis. The equations for preamplifier noise figure are obtained using different models of electronic part of the system. Using these equations, different optimal transformation coefficients are obtained. The optimal transformation coefficients and the noise figure using particular ultrasonic transducers and operational amplifiers are presented.