Hello, I have just started becoming familiar with the FMC150 board, the VHDL, and the Fmc150App reference application. I've been trying to get a handle on the numerous different clock frequencies and clock domains that are routed throughout the FPGA design and on the FMC150 board. I have the standard 491.52MHz VCXO installed. Right now I am primarily focusing on the DAC interface. Could you verify that I have the following default frequencies correct? By "default" I mean that I have not made any changes to the code that is output by the 4FM GUI app. I am interfacing the FMC150 to the Zedboard. The frequencies assume use of the internal 100MHz reference oscillator that is installed on the board. I am using the schematic wire names.
ADC_CLK_P/N (driven by CDCE to ADS62P49): 245.76MHz
CLK_TO_FPGA_P/N (driven by CDCE to FPGA): 245.76MHz
DAC_CLK_P/N (driven by CDCE to DAC3283): 491.52MHz
DAC_DCLK_P/N (driven by FPGA to DAC3283): 245.76MHz
Are those frequencies correct?
From what I have learned from the VHDL firmware code (dac3283_phy.vhd) it appears that a new *pair* of samples (i.e. 1 sample for each of the DAC's outputs) is written out to the DAC from the FPGA at a rate of 122.88MSps. Similarly, the DAC outputs a pair of samples on the analog side at the same rate of 122.88MSps since the DAC3283 is configured for an interpolation factor of 4x which divides the DAC_CLK_P/N frequency by 4. Is this correct?
In addition, with the configuration of the OSERDES (in dac3283_phy.vhd) a new byte (i.e. half-sample) is written into the DAC data interface at an effective rate of 491.52MHz due to a new byte being written out on both the rising and falling edge of the DAC_DCLK_P/N (which is 245.76MHz). Is this correct?
about 6 years ago
You are correct.
an interpolation of 4 means that the output data rate is 4 times faster as the input rate. Therefore the DAC output clock should be 4 times the digital input data rate.
The FPGA to DAC interface transfers data for both the channel A and the channel B as well as two bytes per channel. This is 4 bytes so therefore the data rate on the digital data bus has to be 4 times the actual sample rate.