A New Multistage Noise-Shaping Architecture

Abstract

This paper presents a new architecture for high dynamic range, low oversampling ratio (OSR) noise-shaped digital-to-analog converters (DACs). The instantaneous noise feedforward architecture is a multistage structure in which the instantaneous noise and gain/phase distortion in the first stage are cancelled by passing them through another converter and then subtracting them at the output after analog attenuation. The signal-to-noise-and-distortion ratio (SNDR) of a device using this architecture scales as the product of the first noise shaper's SNDR and the ratiometric precision of the attenuator technology. This new architecture was implemented by driving the bits of an existing DAC (with binary weighting) using specially generated digital signals. One set of experimental measurements demonstrates a spurious-free dynamic range (SFDR) performance of 83 dBc in a 125-MHz bandwidth centered at 325 MHz while using an OSR of only 4. A second set of experimental measurements produces an SFDR performance of 70 dBc in a 125-MHz bandwidth centered slightly above 1.3 GHz with an OSR of 16