A Spur-free Dynamic Element Matching Scheme for Bandpass DACs

Dynamic element matching (DEM) is a popular class of techniques that exploit redundancy to linearize digital-to-analog converters (DACs) in the presence of component mismatches. Most DEM techniques employ spectral shaping of the DAC mismatch error power, often in conjunction with randomization, to suppress in-band error and spurious tones. However, spurious tone elimination is mathematically guaranteed in very few DEM approaches that too only in 1st order high-pass shaping DEM. This paper describes a “reset-and-dither DEM” technique, that can provably eliminate spurious tones in oversampled band-pass DACs in the presence of static component mismatches. The theoretical basis of the technique is outlined and the absence of spurious tones is demonstrated through simulations.

I. Introduction

DYNAMIC element matching (DEM) is a commonly used technique to mitigating non-linearity caused by mismatches in DACs. In most DACs, most of the desired nominal output values can be realized in multiple ways e.g., by selecting different groups of cells. The DEM exploits this redundancy by potentially selecting a different group of cells each time. Data weighted averaging (DWA) [1] accomplishes this by cycling through all available cells in sequence and is known to achieve 1st order high-pass shaping of the DAC mismatch error power. Several variants have been reported including vector shaping [2], tree structured shaping [3], higher order shaping [2], [4], and combined vector shaping and tree structured shaping [5]. Complex versions with in-phase and quandrature paths for use in quadrature band-pass DACs have also been reported [2], [6] [7], [8], [9]. Theoretical conditions that are necessary and sufficient for the DAC noise power spectral density (PSD) to have a certain desired shape have also been reported [10]. The reader is referred to [11] and [12] for comprehensive overview of the subject.