AN ULTRA-LOW-POWER, LOW-VOLTAGE ELECTRONIC AUDIO DELAY-LINE FOR USE IN HEARING-AIDS

In this paper, the design of an electronic audio delay line, realized with a second-order all-pass filter, is presented. The designed filter is primarily intended for use in hearing aids, to provide directivity by a specially designed microphone array, The filter operates at a su pply voltage of as low as 1.8 V, The simulated and measured total quie scent current is 0.9 mu A, Owing to current companding and class-AB op eration, the dynamic range is 62 dB at a total harmonic distortion (TH D) below 7%, i.e., at maximum output, The delay time is adjustable by control currents, The filter has been integrated in a standard bipolar process, The total measured delay time of the all-pass filter is appr oximately 110 mu s over a bandwidth of 4 kHz.