A 18-bit sixth-order sigma-delta modulator for audio application

In this paper a 3.3-V 18-bit sixth-order sigma-delta modulator for audio application is presented. By adopting modifled-sixth-order-feedforward architecture, the proposed modulators avoid additional signal summation at the input of quantizer and the function of the system can be verified in short transient simulation from the output of the fifth integrator. The modulator is designed with fully differential switched capacitor, utilizing a single-loop single-bit output topology. The OPAMP in the integrator is designed to hold relatively constant DC gain over the entire output range to provide high linearity. Moreover, the over-flow detecting technology is employed to detect the stability of the modulator. With an oversampling ratio of 64, the sigma-delta modulator achieves a signal-to-noise ratio of 112 dB over a bandwidth of 20 kHz.