A programmable analog hearing aid system-on-chip with frequency compensation

An analog hearing aid with the function of frequency compensation is proposed and implemented considering the human factors. Introducing the current-mode technique, a filter designed by the state space methodology is integrated in the hearing aid to offer the function which only appears in the DSP unit of digital hearing aid. Combined with the filter embedded in the driver circuit adopting the minimum current selecting technique, the enhance frequency compensation can well match to the common low-frequency hearing loss with a stopband attenuation of 80 dB/dec. Moreover, a low-noise automatic gain control (AGC) is presented to improve the programmability with discreet gains, knee points and compression ratios. To enhance the comfortable level, the attack time and release time is set 20 and 100 ms with a peak detector. The input-referred noise is below 5 μVrms. The hearing aid can drive a 16 Ω receiver at the supply voltage of 1 V. The die area is 2.3 × 1.5 mm2 (AGC) and 0.93 × 0.86 mm2 (driver) in a 0.13 μm standard CMOS process and 1 × 1 mm2 (filter) in a 0.35 μm standard CMOS process.