A 107.5-dB dynamic range 402-μW event-driven dynamic zoom ADC with voice activity detection function for audio applications

This paper presents a dynamic zoom analog-to-digital converter (ADC) for audio applications, which combines a 5-bit coarse event-driven (ED) ADC (also called level-crossing ADC) and a 3rd-order, single-bit discrete-time ΔΣ modulator (ΔΣM). With 2 low-power continuous-time (CT) comparators and a corresponding digital circuit operating only at the event that the input signal crosses the reference levels, the coarse ED ADC consumes much less power than those coarse SAR ADCs operating under the sampling frequency (Fs) in the conventional dynamic zoom ADC schemes, because the ED scheme operates with much less activity and shows higher adaptivity to real acoustic signal applications. Moreover, the ED ADC output can be utilized to generate a voice activity detection (VAD) signal, which provides a simple on-device audio computing function for the analog front-ends in audio applications. A cascoded floating-inverter-amplifier (FIA) based integrator is employed in the fine ΔΣM to reduce power consumption further. Fabricated in a 0.18-μm CMOS process, the prototype ADC chip achieves 102.1-dB peak signal-to-noise ratio (SNR), 103.1-dB peak signal-to-noise-and-distortion ratio (SNDR), and 107.5-dB dynamic range (DR) for a 24-kHz bandwidth and 6.144-MHz Fs, while consuming only 402 μW under the 1.8-V power supply, resulting in a Schreier Figure-of-Merit (FoMs) of 185.3 dB.