NCO Frequency Conversion - 2.6 English

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

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2.6 English

The NCO is in the digital domain and its effective frequency range is always from -Fs/2 to Fs/2.

When the RF-ADC or the RF-DAC operates at sub-sampling frequencies (Fc>Fs/2), the application must first calculate the signal location at the 1st Nyquist band and then set the effective NCO value to shift signals.

For convenience, the Zynq UltraScale+ RFSoC IP GUI and API supports setting the NCO frequency in the range from -10 GHz to 10 GHz (the RFdc API does not have a restriction on the NCO range.). The Vivado Design Suite or RFdc API converts high frequencies outside of the first Nyquist zone to an effective NCO configuration automatically. This works for both RF-ADCs and RF-DACs, and follows the sampling theory strictly.

To avoid the inversion of the original spectrum, set positive NCO frequencies in down conversion when the desired signal is located at even Nyquist bands, or negative NCO frequencies when the desired signal is located at odd Nyquist bands. For up conversion, set negative NCO frequencies when shifting a signal to even Nyquist bands and positive frequencies when shifting a signal to odd Nyquist bands (this conversion only applies when setting the NCO to a frequency outside the first Nyquist bands (±Fs/2).).