Is necessarily to use reference buffer with the AD2S1205/AD2S1210 converter ?
The AD2S1205/AD2S1210 chip has on board reference oscillator which is responsible for producing differential excitation signal. This signal should be feed into the primary coil of the resolver such as resovler can output modulated SIN/COS signals. Because the AD2S12xx device is supplied signle ended with 5 V rail the differential reference output is limited by the supplies. Typically differential signal is 8 Vpp. However, most of todays resolvers require larger signal on their primary coil hence signal often needs to be gained before applied to the sensor. Moreover primary coil has usulaly relatively low resistance which resutls in larger current being present on the input. Therefore, excitation buffer beside providing the gain factor should also be able to drive impedances as low as 100 Ohm.
The AD2S1205/AD2S1210 cannot provide such a current on the excitation outputs therefore excitation buffer is required. It should be noted that ADI provides receommended buffer configuration in the product datasheet however it is possible to use different architecutre.