In this paper a low-power audio ΣΔ modulator under 0.7 V supply is proposed. The proposed structure uses a second order modulator with cascade integrator feedback (CIFB) and half-delayed input-feedforward architectures. In order to avoid the extremely scaling the loop filter coefficients in the CIFB ΣΔ modulator with tracking quantizer, the proposed modulator employs a novel difference-tracking multi-bit quantizer. Since the maximum step size of the proposed quantizer output signal is considered 3VLSB, compared with the conventional counterpart, a larger noise transfer function (NTF) gain can be allowed leading to a considerable reduction in the complexity and power consumption of the modulator. Simulation results of the proposed modulator in a 0.18-μm CMOS technology confirm that an SNDR of 97.9 dB is achieved for a 20-kHz signal bandwidth at the cost of 400 μW power consumption when the supply voltage is only 0.7 V.@en