RF-DAC High Sampling Rates Mode (Gen 3/DFE) - 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 maximum sampling rate of the RF-DAC is defined in the Zynq UltraScale+ RFSoC Data Sheet: DC and AC Switching Characteristics (DS926), and the maximum data rate is limited by the DUC.

To increase the sampling rate, the following two configurations are available:

  1. Bypassing the DUC: the RF-DAC works in Real to Real mode. This configuration achieves sampling rate up to the maximum specified and full bandwidth, but without the DUC functions (interpolation, mixer, multi-band, QMC).
  2. Enabling the DUC: An additional Image Rejection (IMR) interpolation filter stage after the DUC must be enabled. This limits the data rate to the rate specified for IMR mode before the IMR interpolation filter.

RF-DAC mix-mode and the inverse sinc filter (both Nyquist bands) are available for both cases.

The following image illustrates the RF-DAC datapath with the IMR filter.

Figure 1. RF-DAC Datapath with the IMR Filter

The IMR filter can be configured in either high pass or low pass mode. The filters are symmetric with a suppression of 60 dBc and flatness of ±0.01dB in the 80% Nyquist band.

When configuring the IMR filter in low pass mode, the original signal from the DUC is passed to the RF-DAC; when configuring the IMR in high pass mode, the image signal in the 2nd Nyquist band (before 2x interpolation) is passed to the RF-DAC. Note the signal after the high pass filter is an inverse copy of the original signal; inverting the sign of the NCO corrects this.

When the 2x IMR filter is enabled, the available interpolation factors in the RF-DAC high sampling rates mode is listed below:

2x (IMR only), 4x, 6x, 8x, 10x, 12x, 16x, 20x, 24x, 32x, 40x, 48x, 80x