A 120 dB multi-bit SC audio DAC with second-order noise shaping

The 24 b consumer audio formats such as DVD-A make low-cost, high-performance audio converters essential. Multi-bit /spl Sigma//spl Delta/ modulators are the preferred choice for converters achieving high performance, especially in DACs. Compared with continuous-time, current mode DACs, a SC architecture provides significantly higher clock-jitter tolerance and eliminates inter-symbol interference. The performance of conventional 1 b SC DACs is limited by severe post-filtering needs and constrained signal swings due to poor modulator stability. The relaxed filtering needs and better modulator stability of a multi-bit approach make the multi-bit DAC an attractive alternative. However, nonlinearity caused by sampling element mismatch must be overcome to produce a low-distortion device. Second-order dynamic element matching (DEM) is used to address the nonlinearity issue. The second-order DEM technique used here is an improvement on the second-order data weighted averaging (2DWA) DEM technique reported previously. The DAC using this DEM achieves 100 dB THD and -120dB integrated noise over 20 kHz band. The 9.4 mm/sup 2/ chip is fabricated in a 0.35 /spl mu/m DPTM CMOS process. The analog part operates on a 5 V supply and the digital part operates at both 3.3 V and 5 V. The chip consumes <200 mW when the digital part operates at 3.3 V.