Comparison of High-Order Programmable Mismatch Shaping Bandpass DEM Implementations Applicable to Nyquist-Rate D/A Converters

Abstract

Non-shaping dynamic element matching (DEM) randomization schemes are widely adopted for wideband Nyquist-rate digital-to-analog converters (DACs) within transmitter architectures. Here, randomization translates the mismatch-induced distortion into white noise from dc to $\text{F}_{\mathrm{ s}}$ /2 range. However, the DAC performance for various bands within the Nyquist range cannot be improved using non-shaped DEMs as their inherent structure cannot be made programmable. Conversely, mismatch-shaping DEMs can be made tunable to shape the DAC errors over various signal bands, which makes them suitable for wireless transmitter applications. This paper presents the design methodology for high-order mismatch-shaping DEM architectures suitable for wideband Nyquist DACs. The challenge in designing high-order DEM structures for Nyquist DACs is to make them programmable to cover various signal bands within the Nyquist range and to operate them at high-frequencies demanded by the applications. Moreover, the stability of the high-order loop-filter within the DEM and its implementation cost is of great concern. This work details techniques to design programmable, stable, and hardware efficient high-order DEM structures for wideband Nyquist DACs. The DEM structures are implemented on an UltraScale+ FPGA device for prototyping and validation. Furthermore, the DEM design operation is validated by obtaining the measurement results interfacing with a 5-bit analog DAC.

Keywords

• Bandpass
• current-steering
• DEM
• Nyquist-DAC
• programmable