A low-voltage low-power analog controllable preamplifier for electret
microphones is presented. It has been designed for a single supply vol
tage of 1.0 V, whereas its average power consumption amounts to some t
ens of microwatts. A de current controls its gain directly into decibe
ls. The design meets specifications (listed in Section I) concerning a
ccuracy, bandwidth, noise properties, etc., suitable for most applicat
ions in portable telephone equipment, portable transceivers, hearing a
ids, etc. Much attention has been paid to the dynamic range of the inp
ut signal, noise, and offset properties. The circuit has been realized
in a semi-custom IC process. Simulation and measurement data of the m
ost important properties are presented.