Wa. Serdijn et al., A LOW-VOLTAGE LOW-POWER FULLY-INTEGRATABLE FRONT-END FOR HEARING INSTRUMENTS, IEEE transactions on circuits and systems. 1, Fundamental theory andapplications, 42(11), 1995, pp. 920-932
In this paper, the front-end of a universally applicable analog integr
ated circuit for hearing instruments is presented. This IC comprises t
he following functions: a microphone preamplifier, a pickup-coil pream
plifier, a second-order high-pass filter and a second-order low-pass f
ilter, both with a controllable cutoff frequency, and an input-control
led automatic gain control with an adjustable knee level, By applying
a compression/expansion system and operating all the circuits in the c
urrent domain as much as possible, all these functions can be implemen
ted 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 BICM
OS process (using only vertical NPN's and lateral PNP's) amounts to 2.
4 mm(2).