Method and apparatus for extending the spurious free dynamic range of a digital-to-analog converter

Abstract

A DAC system provides an expanded SFDR when compared to the SFDR of an individual DAC(s) that makes up the DAC system. The DAC system uses a clipping arrangement which receives the digital input signal and provides an amplitude-limited signal and resulting signal distortion to a first DAC for digital input signals whose amplitudes would result in an insufficient SFDR for the first DAC. By amplitude-limiting the digital input signal, the amplitude of the digital input signal is effectively reduced or “clipped,” thereby improving the SFDR performance for the first DAC. The signal distortion resulting from the amplitude adjustment is routed to a second DAC. The first DAC converts the amplitude-limited digital signal to an analog signal with an expanded SFDR due to the lower amplitude of the adjusted digital signal. The second DAC receives the signal distortion which can be viewed as the clipped amplitude portion of the digital input signal. The second DAC converts the signal distortion, which typically has a lower amplitude than the adjusted digital signal, to an analog signal with at least an acceptable SFDR. The DAC system combines the resulting analog signals from the first and second DACs to produce the desired converted analog signal with an increased relative difference between the amplitudes of the output signal and the spurious distortion, thereby providing an extended SFDR for the DAC system when compared to the SFDR if the digital input signal had been converted by the first DAC without amplitude adjustment.