An Ultra-Low-Power, Low-Noise, Linear Preamplifier with Wide Dynamic Range for Electret Microphones

The microphone preamplifier forms a critical stage for signal detection and pre-processing within hearing aids and cochlear implants. In this paper, a micro-power, low-noise enhanced linear preamplifier with wide dynamic range for electret microphones is presented. Current-sensing topology is used instead of the usual voltage-sensing of the microphone. The design employs an ultra-low-power, wide-linear-range trans-conductance amplifier as a DC cancellation feedback loop to prevent output saturation and increase linearity. The proposed preamplifier is designed and simulated in a 0.18 μm CMOS process. The overall circuit exhibits a varying dynamic range from 100.5 dB to 80.47-dB with 1 μVrms of total input-referred noise from 100 Hz to 10-kHz. The power consumption is 5.8 μW (excluding the microphone and biasing circuits) while operating from a single 1.8 V power-supply. The in-band power-supply rejection ratio (PSRR) is about 60 dB and the in-band total harmonic distortion (THD) varies from -80 dB to -40 dB for 20 mVp-p output.