LOW-POWER HIGH-SPEED AMPLIFICATION USING FILTERBANK FOR DIGITAL HEARING AIDS
Keywords:Filter bank, hearing aid, low group delay.
The ANSI S1.11 1/3-octave filter bank is suitable for digital hearing aids, but its large group delay and high compu- tational complexity complicate matters considerably. This study presents a 10-ms 18-band quasi-ANSI S1.11 1/3-octave filter bank for processing 24 kHz audio signals. We first discuss a filter order optimization algorithm to define the quasi-ANSI filters. The group delay constraint of filters is limited to 10 ms. The proposed design adopts an efficient prescription-fitting algorithm to reduce inter-band interference, enabling the proposed quasi-ANSI filter bank to compensate any type of hearing loss (HL) using the NAL-NL1 or HSE prescription formulas. Simulation results re- veal that the maximum matching error in the prescriptions of the mild HL, moderate HL, and severe-to-profound HL is less than 1.5 dB. This study also investigates the complexity-effective multirate IFIR quasi-ANSI filter bank. For an 18-band digital hearing aid with a 24 kHz sampling rate, the proposed architecture eliminates approximately 93% of the multiplications and up to 74% of the storage elements, compared with a parallel FIR filters architec- ture. The proposed analysis filter bank (AFB) was designed in UMC 90 nm CMOS high-VT technology, and on the basis of post-layout simulations, it consumes 73 W. By voltage scaling (to 0.6 V), the simulation results show that the power consumption decreases to 27 W, which is approximately 30% of that consumed by the most energy-efficient AFB available in the literature for use in hearing aids.
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