RF-DAC Data Pattern

Data patterns with the TDMS or LVM file format are available for reference under \Data\DAC\. The content of these files are not intended to be compliant to any standard. The files are provided as example waveforms that can be used to create files for your application. The contents of these files can be easily identified from the file name. Here is an example of a file name, IQ_1x_QAM256_RRC0p1_50M_BB491p52MHz_length_16M_-15dB.tdms.

This file name means that the data pattern is in IQ (complex) format, there is one QAM256 modulated carrier, the RRC roll-off coefficient is 0.1, carrier bandwidth is 50 MHz, data sampling rate is 491.52 MHz, data length is around 16M samples, carrier amplitude is –15 dBFS, and the file format is TDMS. Configure RF-DAC in IQ mode at the digital side, set the RF-DAC sampling clock at 3932.16 MSPS, set the interpolation factor as 8 (491.52M * 8 = 3932.16 MHz), then load this file from the RF-DAC FFT page, and you will see the correct carrier.

Note: For the ZCU111 board, the maximum number of samples that the block RAM can handle is 32K for IQ data and 64K for real data. For the ZCU208 and ZCU216 boards, the maximum number of samples that the block RAM can handle is 8K for IQ data and 16K for real data. Switch to the DDR mode (in Memory Type) for data sources if the number of samples is greater than this limitation.

The following figure illustrates the FFT plot of this carrier captured by RF-ADC with a loopback path using the ZCU111 board. In this example, the RF-DAC is set in 32 mA/3V mode and some digital gain has been used to increase the carrier amplitude seen by the RF-ADC.

Figure 1. RF-DAC Test Pattern Example

Note: If the DAC vector length is larger than 1M samples (e.g., being driven by DDR), the GUI tool rounds to this limit for display purposes only. This might lead to the impression that the signal is not coherent, due to rounding, but this is only a visual display artifact.