A 1-V 25-µW low-noise CMOS programmable gain pre-amplifier for digital hearing aid

A low-voltage low-noise programmable gain pre-amplifier (PGA) is presented in this paper. The proposed PGA is based on a fully-differential source-degeneration structure with g_m-boosting circuitry. The design is implemented in UMC 0.18um CMOS process and occupies an active area of 0.128 × 0.08 mm². It dissipates only 25-μW from a single 1-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/√Hz at 1kHz, the white noise is 16.4 nV/√Hz and the integrated noise in the audio range (20~20kHz) is 3μV.