A 147-dB dynamic range electronic attenuator for audiometric applications with on-chip 1-W power amplifier

Abstract

This paper presents an integrated circuit for audiometric applications, which includes a linearly controlled exponential attenuator with 147 dB of dynamic range and a power amplifier capable of driving 8 V/sub pp/ on a 7-/spl Omega/ resistive load. The required attenuation is achieved in the current domain by exploiting the exponential transfer characteristic of bipolar transistors. In order to achieve a temperature-independent attenuation, in spite of the temperature-dependent bipolar transistor I/sub C/-V/sub BE/ relationship, we produce on-chip an attenuation control voltage proportional to the absolute temperature. The 24-mm/sup 2/ chip, fabricated in a 2-/spl mu/m high-voltage CMOS process, achieves the required dynamic range with 80 dB of spurious-free dynamic range (excluding harmonics) and -57 dB of total harmonic distortion, consuming 33 mA from a /spl plusmn/5-V power supply.