Linearity enhancement of multibit ΔΣ modulators using pseudo data-weighted averaging

The occurrence of inband signal-dependent tones, when using data-weighted averaging (DWA) in multibit ΔΣ modulators, degrades the spurious-free dynamic range and can preclude using DWA at low oversampling ratios (OSR). This paper proposes a simple technique, called Pseudo DWA, to solve the tone problem in DWA. Pseudo DWA is implemented in a 3rd-order ΔΣ A/D converter with a 32-level internal D/A converter (DAC), a 16x OSR, and a 2-MHz conversion bandwidth. Simulations show that, with a 0.5% DAC element mismatch, Pseudo DWA attenuates the DWA tones at the cost of only 1-dB drop in the signal-to-noise ratio. Existing techniques are also compared using simulations.