Abstract: A third-order low-power ΣΔ modulator for a high-end 18bit audio-band analog-to-digital converter is developed.The modulator is based on a 2-1 cascaded architecture with optimized coefficients to extend the dynamic range and reduce the spectrum tones.The gate-source bootstrapping technique is employed to enhance the sampling switch linearity.A power-efficient class A/AB operational transconductance amplifier (OTA) is proposed,which achieves a high slew rate of 100V/μs with only 0.8mA current consumption.The OTA designed for the second and third integrators is a scaled version of the first OTA,which allows for further power reduction.The modulator is implemented in SMIC mixed-signal 0.18μm CMOS technology,and the area is 1.1mm × 1.0mm.Experimental results indicate a peak signal-to-noise-and-distortion ratio (SNDR) of 91dB and a dynamic range of 94dB over a 22.05kHz bandwidth.The chip operates under a 3.3V power supply with a power dissipation of 6.8mW,which is suitable for high-performance,low-power audio ADC applications.

Key words: ΣΔ modulator, gate-source bootstrapped, low power, audio analog-to-digital converter