New Harmonic-Distortion-Suppression Method

Abstract

This section presents a method to improve the linearity of current steering (CS) digital-to-analog converters (DACs). The method uses unary functional segmentation to create redundant D/A functions, defined around nominally identical sub-DAC entities. Further, the method uses a digital pre-processor to create phase shifted replicas of the input signal that are fed to the sub-DACs. These represent the input arguments for the redundant D/A functions. The parallel sub-DAC branches convert the input signal replicas to currents. The output currents are combined and their harmonic distortion components mutually suppress each other. In this way, the overall DAC spurious-free-dynamic-range (SFDR) and total-harmonic-distortion (THD) are improved. The method can be applied with either a single conventional CS DAC, based on emulated virtual parallel sub-DACs, or a CS DAC with unary functional segmentation, i.e. based on physically present parallel sub-DACs. The method is particularly suitable for OFDM communication systems and mixed-signal systems-on-a-chip with DACs, e.g. FPGAs with integrated DACs. Recently, a similar method has been developed for the RF field, in an independent research project [61], which further advocates in favor for applying this approach in the field of DACs.