Efficient FSK/PSK Modulator Uses Multichannel DDS to Switch at Zero Crossings

This article describes how two synchronized DDS channels can implement a zero-crossing FSK or PSK modulator. In phase-coherent radar systems, zero-crossing switching reduces the amount of post processing needed for target signature recognition; and zero-crossing switching reduces PSK spectral splatter. Here, the AD9958 two-channel complete DDS is used to switch at the zero crossing.