RF-DAC Nyquist Zone Operation - 2.6 English

Zynq UltraScale+ RFSoC RF Data Converter v2.6 Gen 1/2/3/DFE LogiCORE IP Product Guide (PG269)

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2.6 English

Each RF-DAC can optimize its output response in the second Nyquist zone by using the mix-mode feature. This feature mixes the RF-DAC data with the sample clock, and, as a result, increases the output power in the second Nyquist zone, while attenuating it in the first Nyquist zone. This is shown in the following figure.

Figure 1. RF-DAC Nyquist Zone Operation

For normal (non-mix mode) operation, the blue line represents the ideal RF-DAC output roll-off sinc response. As can be seen, an output image in the second Nyquist zone in this mode would be severely attenuated. An inverse sinc filter is available to compensate for the roll-off in the first Nyquist zone for this mode. See RF-DAC Inverse Sinc Filter for more information.

In RF-DAC mix-mode, the red line represents the ideal RF-DAC output response. In this mode, the output power of the image in the second Nyquist zone is significantly increased, and it also has an approximately flat response across the majority of the zone. The Nyquist zone can be set in the Vivado IDE. Operating the RF-DAC in Nyquist zones higher than 2 is typically not used due to the sinc response attenuation and possible bandwidth roll off.