A 0.9-V 67-/spl mu/W analog front-end using adaptive-SNR technique for digital hearing aid

An analog front-end composed of a preamplifier and a /spl Sigma/-/spl Delta/ modulator is proposed and implemented for digital hearing aid chip. The combined gain control (CGC) 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 /spl Sigma/-/spl Delta/ 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-/spl mu/W. In case of /spl Sigma/-/spl Delta/ modulator, the peak signal-to-noise ratio (SNR) is 86-dB, the average power consumption is 31.4-/spl mu/W and the variation of SNR is 14-dB. The proposed analog front-end dissipates less than 67-/spl mu/W from a single 0.9-V supply. The core area of the preamplifier and the /spl Sigma/-/spl Delta/ modulator is 0.1-mm/sup 2/ and 0.4-mm/sup 2/, respectively, in a 0.25-/spl mu/m standard CMOS technology.