w-Voltage Low-Power Fully-Integratab t-End for Hearing Instruments

In this paper, the front-end of a universally applicable analog integrated circuit for hearing instruments is presented. This IC comprises the following functions: a microphone preamplifier, a pickup-coil preamplifier, a second-order high-pass filter and a second-order low-pass filter, both with a controllable cutoff frequency, and an input-controlled automatic gain control with an adjustable knee level. By applying a compressiodexpansion system and operating all the circuits in the current domain as much as possible, all these functions can be implemented in a single IC, without the need for external components. The test chip demonstrates operation down to 1.05 V and a current consumption between 120 and 175 PA. The full-custom chip area in a 2.5-pm BiCMOS process (using only vertical NPN’s and lateral PNP’s) amounts to 2.4 mm’.