Analogue VLSI implementation of a 2-D sound localisation system
The position of a sound source can be accurately determined in both azimuth and
elevation through the use of localisation cues extracted from the incident audio signals.
Compared to lateral localisation, 2-D hardware localisation is novel and requires the
extraction of spectral cues in addition to time delay cues. The objective of this work is to
develop an analogue VLSI system which extracts these cues from audio signals arriving
at the left and right channels of the system, and then map these cues to the source
position. The use of analogue hardware, which is broadly adapted from the biological
auditory system, enables fast and low power computation.
To obtain accurate 2-D localisation from the hardware-extracted cues a novel
algorithm for the mapping process has been developed. The performance of this algorithm
is evaluated via simulation under different environmental conditions. The effects of
hardware non-idealities on the localisation accuracy, including mismatches and noise are
The analogue hardware implementation is divided into three main sections: a
front-end for splitting the input signal into different frequency bands and extraction of
spectral cues, an onset detector for distinguishing between the incident portion and the
echo portion of the acoustic signal, and a correlator for determination of time delay cues.
Novel building blocks have been designed using standard CMOS in order to enable low
voltage low power operation of the differential architecture essential for the accuracy of
the extracted cues. A novel feedback technique enables accurately controlled Class AB
operation of a low voltage switched-current memory cell. A novel cross-coupling
technique ensures correct Class AB operation of a log-domain bandpass filter. The five
chips developed here operate at ± 0.9 V supply. The system has been tested by applying
audio signals convolved with a position-dependent transfer function at the input, and then
processing the resulting hardware-generated cues. Measurement results show that 2-D
localisation within 5° accuracy is achievable using hardware extracted cues.
Key words: sound localisation, analogue VLSI, silicon cochlea, log domain, switched
capacitor, switched current, current mode, analogue processing.