A 300-μW Audio Δσ Modulator with 100.5-dB DR Using Dynamic Bias Inverter

This paper presents a micropower audio delta-sigma (ΔΣ) modulator for mobile applications. This work employs power-efficient integrators based on the dynamic bias inverter, which consists of a cascode inverter, a floating current source and two offset-storage capacitors. The quiescent current of the inverter is copied from the floating current via offset-storage capacitors and the speed limitation caused by the cascode transistors in the inverter is resolved by using active parasitic compensation. This maximizes both gm/ID ratio and slew rate of the inverter-based integrator, while compensating process, voltage, and temperature (PVT) variations. To verify the effectiveness of the proposed technique, a single-bit third-order ΔΣ modulator is implemented in a 0.18 μm CMOS technology. The prototype modulator achieves 97.7 dB SNDR, 98.6 dB SNR, and 100.5 dB DR in a 20-kHz signal bandwidth, while consuming only 300-μW from a 1.8 V supply. This corresponds to a state-of-the-art Schreier's FoM of 178.7 dB. The results are fully verified under variable supplies and temperatures.