A 0.9-V 67-µW analog front-end using adaptive-SNR technique for digital hearing aid

An analog front-end composed of a preamplifier and a Σ-∆ modulator is proposed and implemented for digital hearing aid chip. Combined gain control (CGC), the technique, which incorporates an automatic gain control (AGC) with an exponential gain control (EGC), is employed to enlarge dynamic range and reduce power consumption. The proposed Σ-∆ modulator exploits adaptive-SNR technique, which generates four different SNRs, thereby achieving low power consumption and optimizing performance. The measured power dissipation of the preamplifier is 35-μW. In case of Σ-∆ modulator, the peak signal-to-noise ratio (SNR) is 86-dB, the average power consumption is 31.4-μW and the variation of SNR is 14-dB. The proposed analog front-end dissipates less than 67-μW from a single 0.9-V supply. The core area of the preamplifier and the Σ-∆ modulator is 0.1-mm and 0.4-mm, respectively, in a 0.25-μm standard CMOS technology.