A Bandwidth-Adaptive Preamplifier

We propose an adaptive microphone preamplifier that adjusts its power consumption according to the input signal´s bandwidth. A chip prototype of the adaptive preamplifier for speech processing was fabricated in a 0.5-μm CMOS process. The adaptive preamplifier´s measured input referred noise is 3 μV rms and its total harmonic distortion is -40 dBc for an 80-mV rms input amplitude. These noise and distortion specifications remain virtually constant over the preamplifier´s range of bandwidth adaptation. The adaptive preamplifier consumes 65 μW of power. This is achieved with no degradation in speech quality, when compared to a conventional preamplifier of fixed bandwidth, and as measured by the perceptual evaluation of speech quality (PESQ) score.