Multichannel DDS Enables Phase-Coherent FSK Modulation

Common single-channel direct-digital synthesizers produce phase-continuous frequency transitions. In Doppler radar, NMR/MRI spectrometry, and other applications, however, phase-coherent transitions are preferred. This article demonstrates how to configure the AD9958/AD9959 multichannel DDS as a robust phase-coherent frequency-shift keyed (FSK) modulator by summing the DDS outputs.