Reducing Transformerless Microphone Preamplifier Noise at Low Gain Settings

摘要

This paper considers the noise performance of microphone preamplifiers at low gain setting. A detailed noise analysis of the classic current-feedback instrumentation amplifier topology often used for transformerless microphone preamplifiers is presented. The noise contributors that are significant at low gain settings are identified. Several techniques to reduce their magnitude are discussed. One novel technique is introduced that is easily implemented at very low cost and requires a modest increase in power consumption only. Furthermore, it offers a benefit with respect to the frequency response and distortion performance of the circuit. The theoretical results are verified with experimental measurement data.