A 1-V 25-μW Low-Noise CMOS Programmable Gain Pre-Amplifier for Digital Hearing Aid

A low-voltage low-noise programmable gain preamplifier (PGA) is presented in this paper. The proposed PGA is based on a fully-differential source-degeneration structure with gm-boosting circuitry. The design is implemented in UMC 0.18um CMOS process and occupies an active area of 0.128 x 0.08 mm(2). It dissipates only 25-mu W from a single I-V supply. The total harmonic distortion (THD) is below -50dB over the audio frequencies at 0.2-Vpp differential output. The single-stage gain ranges from 12dB to 27dB in 3dB step with a gain error of less than 0.4dB. When set at the max gain, the equivalent input noise is 25 nV/root Hz at 1kHz, the white noise is 16.4 nV/root Hz and the integrated noise in the audio range (20 similar to 20kHz) is 3 mu V.