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A 94dB SFDR 78dB DR 2.2MHz BW Multi-bit Delta-Sigma Modulator with Noise Shaping DAC

A 94dB SFDR 78dB DR 2.2MHz BW Multi-bit Delta-Sigma Modulator with Noise Shaping DAC. Application: For high SNR and SFDR, such as xDSL and Hi-Fi audio. Preferred architecture : Multi-bit ∆Σ M (Delta-Sigma Modulator). Problem : Nonlinear DAC in the feedback loop degrades the performance.

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A 94dB SFDR 78dB DR 2.2MHz BW Multi-bit Delta-Sigma Modulator with Noise Shaping DAC

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  1. A 94dB SFDR 78dB DR 2.2MHz BW Multi-bit Delta-Sigma Modulator with Noise Shaping DAC 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. Nonlinear 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 DSM is degraded. • In conclusion: The DEM improves SFDR, but degrades SNR. In other words, it trades SNR for SFDR.

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

  3. No input signal • DAC thermal noise is shaped • Reference noise is also shaped 94dB NSDEM is off NSDEM is on Noise floor is limited by switches thermal noise of input signal path • 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 DSM chip meets the specification for ADSL2+.

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