An 0.8-μm CMOS mixed analog-digital integrated audiometric system

This paper presents a dual-channel fully integrated audiometric system, which generates the complete set of audio and control signals required for exhaustive audiometric tests. The system includes a novel signal generator, based on the direct digital synthesis technique, which fulfils the requirements of advanced audiometric tests. The proposed system faces two different problems, namely, the generation of a finely tunable pure sinewave and the generation of noise signals with a controlled spectrum. To achieve tuning capabilities down to 1 Hz at 20 kHz and 15 μHz at 100 Hz, a fractional division of a 40-MHz master clock based on noise-shaping techniques is performed. Moreover, for noise generation, a novel circuit based on pseudorandom sequences combined with analog switched-capacitor filters is used. The chip is fabricated in a 0.8 μm CMOS process and occupies a 24.2 mm² silicon area. It consumes 45 mW from a single 5 V power supply and achieves less than -90 dB crosstalk between the channels