I'd like to use the EVAL-ADF4355-2 board as a VCO with an analogue input that can sweep the frequency. My system produces an analogue signal, and I'd rather not go for the complicated option of adding an arduino or something to convert this to a digital signal to interface with the registers.
As far as I can tell there are 2 options. Could you please advise me on what you think the best one is (or provide a better idea), and answer a couple of questions related to them?
My ideas are:
- Providing an external reference frequency from a function generator or similar and using an analogue input to sweep that. It seems that using an external reference requires the internal reference to be disconnected by unsoldering a resistor, is that correct? Also, how well would the board be able to follow changes in the reference frequency?
- Simply attaching an analogue signal to the VTUNE input on the board. I understand that the second option would probably remove the PLL functionality, but that's not necessary for my application. I'm unsure if simply soldering a wire would work, is there anything else that would need to be done to disconnect the PLL? Also, while I found a graph for the sensitivity of the VCO system as a function of frequency in the datasheet for the ADF4355-2, I was unable to find the absolute voltage values that should be used there, is that information available?