I am designing a DDS (max 42.5MHz – thanks DJT) based on an AD9850 module. This module outputs a 0.5V pk-pk sine wave, which I wish to amplify, ideally to a level selectable by the user. I have a very high speed precision op-amp which is running on +-13V.
Originally I was thinking of using two pots (one for offset and one for amplitude). IDK if this would work at all, but if I could I would prefer multi-turn wirewound pots for fine control. This would be ideal if it works, however I am conscious that a 5 or 10 turn pot at 42.5MHz is probably a very high impedance (please correct me if I'm wrong) inductor.
My questions: will it work with a 5 turn wirewound pot (or a crusty one turn pot)?
If not, I suppose I will have to use ganged switches or something to choose between 1.8V/3.3V/5V/10V and AC/DC.
EDIT: Actually, this whole thing is controlled by a micro so I could put in several relays and switch in the gain resistors / DC blocking cap.
EDIT 2: If one can buy a high bandwidth digipot, maybe that could be a solution.
EDIT 3: What about a 74HC4051? Only just found it when googling...