Im using AD9742 (Analog Device) for building a high speed digital-to-analog convertor (DAC). I will use FPGA digital I/O ports as inputs to the DAC. As I can found in the data sheet, the example layout could be found and shown in the figure below.
I can understand the R1-R9 are the pull-down resistors to make the inputs at GND level in case there are no inputs (floating).
I can't figure out what are the purposes for using RP3 and RP4 (22-ohm) in series between DB0X-DB13X to DB0-DB13 before DAC inputs.
I have searched other kinds of DAC data sheet (ex. TI DAC902, DEM-DAC90xU/E) and they all have similar design. Does anyone know why we need the RP3 and RP4?
Thanks in advance.