A LOW-VOLTAGE LOW-POWER FULLY-INTEGRATABLE FRONT-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 compression/expansion 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 mu A, The full-custom chip area in a 2.5-mu m BICMOS process (using only vertical NPN's and lateral PNP's) amounts to 2.4 mm(2).