A CMOS amplifier with digital gain control for the hearing impaired

This CMOS transadmittance amplifier is designed for use in either an in-the-ear (ITE) or a behind-the-ear (BTE) hearing aid. It will be driven by a pressure-to-voltage transducer (microphone), and it will provide an output current to drive either a current-to-pressure transducer (speaker) or a current-to-magnetic field transducer (coil). It can be used to transduce an input sound pressure level (SPL) into an amplified SPL or into a proportional magnetic field. Amplified sound signals can thus be applied to the middle ear by either acoustic or magnetic coupling. A unique gain control activated by means of a pressure-sensitive capacitance switch provides an advantage over existing rotary gain controls.<>