Xilinx PRODUCT SPOTLIGHT
UNBOXING THE ZYNQ
®
ULTRASCALE+
™
ZCU111
EVALUATION KIT
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RF-DAC
Unlike the ADC, the DAC has only one title type. This
contains quad RF-DACs, and a phase-locked loop to
provide a common clock to all converters within the tile.
Like the ADC tile, the RF-DACs can be configured for a
real output individually or paired to provide an I/Q output
capability.
Another difference with the RF-ADC tile is the RF-DAC
analog outputs. Unlike the RF-ADC inputs, which are
voltage-driven, the RF-DAC outputs are differential current
buffers. This differential output can also be AC coupled
using capacitors or DC coupled. The output current is
configurable to be either 20mA or 32mA. The termination
voltage supplied will change depending upon the current
required.
Clocking & Synchronization
One of the more complex issues in RF signal processing is
the distribution of the clocking network. Each tile provides
a differential clock input within the RFSoC. This clock can
be used to clock the RF-ADC or RF-DAC directly, or it
can be connected straight to the tile PLL to generate the
required sampling frequency.
To assist with synchronization, each RFSoC also provides
an SYSREF pin pair. This can be used to enable multiple
tiles and multiple device synchronizations if required. The
synchronization between tile and devices uses a simplified
version of JESD204B SYSREF, which is popular to
synchronize discrete devices.
Multi-Nyquist Operation
Data converters used in the RFSoC ADC and DAC tiles
are designed to operate across both the first and second
Nyquist zones. The first Nyquist zone is where signals
Xilinx Zynq
®
UltraScale+
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MPSoC
ZCU104 Evaluation Kit
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MPSoC
ZCU106 Evaluation Kit
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fall between 0 and Fs/2, while the second Nyquist zone
falls between Fs/2 and Fs. By careful selection of the
numerically controlled oscillator, it is possible to down-
convert from higher Nyquist zones provided the full
bandwidth is supported.
When working with the RF-DAC, it is also possible to use the
NCO to provide up-conversion and work across the first and
second Nyquist zones. To support this, the RF-DAC enables
the use of a mix-mode output to increase the power available.
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