An Ultra-Low-Power Polarity-Coincidence Feedback Time-Delay-to-Digital Converter for Sound-Source Localization
Daniel de Godoy, Peter R. Kinget · IEEE Journal of Solid-State Circuits · 2019
The time-delay between audio signals in a microphone array is the most important feature for sound-source localization. This article presents a polarity-coincidence, adaptive time-delay estimation (PCC-ATDE), a mixed-signal technique that uses 1-bit quantized signals and a negative-feedback architecture to directly determine the time-delay between signals in the analog inputs and convert it to a digital number. This direct conversion, without a multi-bit analog-to-digital converter and further digital-signal processing, allows for ultra-low power consumption. A prototype chip in 0.18-um CMOS with four analog inputs consumes 78 nW with a three-channel 8-bit digital time-delay output while sampling at 50 kS/s with a 20-us resolution and 6.06 ENOB. We present a theoretical analysis for the non-linear, signal-dependent feedback loop of the PCC-ATDE. A delay-domain model of the system is developed to estimate the power-bandwidth of the converter and predict its dynamic response. Results are validated with experiments using real-life stimuli, captured with a microphone array, that demonstrates the ability of the technique to localize a sound source. The chip is further integrated into an embedded platform and deployed as an audio-based vehicle-bearing IoT system.