1. Application: For high SNR and SFDR, such as xDSL and Hi-Fi audio. Preferred architecture: Multi-bit ∆ΣM (Delta-Sigma Modulator). Problem: Nonlinear DAC in the feedback loop degrades the performance. A 94dB SFDR 78dB DR 2.2MHz BW Multi-bit Delta-Sigma Modulator with Noise Shaping DAC Existing solution  Pros: DEM randomizes the mismatch in DAC and spread the energy of the toned noise to the entire band. Thus, the nonlinearity is improved and the SFDR is increased.  Cons: The spread noise increases the noise floor, and hence the in-band noise power. SNR of the  M is degraded.  In conclusion: The DEM improves SFDR, but degrades SNR. In other words, it trades SNR for SFDR. Nonlinear DAC

2.  1 st -order shaping to DAC noise  DEM reduces tones  Noise shaping DAC or NSDEM improves both SFDR and SNR Proposed Lowpass  M with Noise Shaping DAC Differentiator Accumulator U(z) V(z) H D (z) Quantizer DAC with NSDEM DAC Noise D(z) Quantiazation Noise Q(z) H(z) DEM H I (z) DAC + H D (z) 5th-order 4-bit Quan. lowpass  M with NSDEM H I (z) DEM (PDWA) Quantizer H(z) – loop filter

3. 94dB Signal Bandwidth2.2MHz Clock Frequency35.2MHz SFDR / DR94dB / 78dB Peak SNR / SNDR77dB / 69dB Input Range5.04V pp (differential) Power Consumption62mW @ 3.3V Supply Technology0.35μm CMOS Noise floor is limited by switches thermal noise of input signal path  No input signal  DAC thermal noise is shaped  Reference noise is also shaped NSDEM is off NSDEM is on  Unlike most of the existing DEMs that trade SNR for SFDR.  NSDEM improves both DAC SFDR and SNR.  NSDEM shapes the inherent DAC thermal noise.  Fabricated  M chip meets the specification for ADSL2+.