I am interested in using a number of AD2S1210 RDCs on a board to digitize a few channels of resolver data as well as a few channels of Inductosyn data. Unfortunately the Inductosyns have a significant phase shift, 90 degrees, and thus require special handling. With other converters I would simply shift the reference signal going to the converter to accommodate the Inductosyn phase shift, but that is not possible with the AD2S1210 because of the internal connection between the reference generator and the internal demodulation circuitry.
In some applications of my circuit I would have four channels running at the same frequency and in that case I know that I can simply use the /RESET line on the Inductosyn AD2S1210 chips to get the correct phase relationship. The question is whether there is a deterministic relationship between releasing the /RESET line and the start of excitation? Does the excitation always start at zero phase?
In other applications two channels might be running at one frequency and two at quite another, say 10KHz for the Inductosyns and 1KHz for the resolvers. In those cases I cannot differential synchronization to handle the phasing. Is there some other convenient option to handle the dramatic phase shift seen in Inductosyns in this sort of application? Obviously I could use an extra AD2S1210 just to generate the excitation, but that seems a rather expensive option for what should be a simple problem.
Suggestion for future products - offer a phase register that represents the offset between the internal phase and the external excitation. Then any and all phase relationships can be accommodated without requiring hoop-jumping to synchronize. This should be a nearly trivial feature to add and helpful in a lot of applications. Even some multi-speed resolvers end up with phase shifts over your 44 degree limit.
As long as we are discussing Inductosyns, does ADI have any reference designs for Inductosyn preamplifiers?
I have seen mention of 180 degree flips with disconnect and reconnect as well as some mentions that this part does not exhibit that problem. Does, in fact, the AD2S1210 exhibit the potential for 180 degree angle flips on disconnect / reconnect? If so it represents a considerable risk and issue for systems with slip-rings.