VERDI - AN ACOUSTICALLY PROGRAMMABLE AND ADJUSTABLE CMOS MIXED-MODE SIGNAL PROCESSOR FOR HEARING-AID APPLICATIONS

A CMOS mixed-mode fully-differential signal processor (VERDI), that co nstitutes the core of a hearing aid system, is introduced. Its charact eristics (frequency response, compression level, and output sound pres sure level) are wireless controlled by means of dual tone multi-freque ncy (DTMF) encoded signals transmitted by an external unit. A system d escription is provided, and the implementation and experimental result s of the key components (preamplifier, antialiasing filter, automatic gain control, filter section, output amplifier, and DTMF receiver/deco der) are covered in more detail. The circuit has been fabricated in a conventional 1.2 mu m CMOS n-well process and operates from a single 1 .3 V battery, although a dc/dc converter is required. It consumes typi cally less than 1 mA and occupies 28 mm(2) of silicon. The dynamic ran ge is larger than 66 dB for the maximum input signal (54 mV(rms) = 108 dB SPL).