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

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_pp on a 7-Ω 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_C-V_BE relationship, we produce on-chip an attenuation control voltage proportional to the absolute temperature. The 24-mm² chip, fabricated in a 2-μm 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 ±5-V power supply