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 supply voltage of as low as 1.8 V. The simulated and measured total quiescent current is 0.9 /spl mu/A. Owing to current companding and class-AB operation, the dynamic range is 62 dB at a total harmonic distortion (THD) 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 approximately 110 /spl mu/s over a bandwidth of 4 kHz.