AD2S1210 input signal conditioning for 5 wire resolver

Question

Hello everyone. 
 I have used te AD2S1210 in several projects along with a common 6 wire resolver (EXHI, EXLO, SIN, SINLO, COS, COSLO) without any problem using the excitation buffer suggested in the datasheet and the following input stage with the appropiate optional values to meet the input range of the IC. 
 However, now i have to work with a 5 wire resolver, where SINLO and COSLO are tied together internally, i have tried to use the same approach but is not working at all, randomly activating multiple error flags in the fault register (LOT, DOS mismatch threshold and other bit i do not remember). Here you have a LTSpice capture of the actual circuit i am trying to use: 
 Analyzing signal received by the ADS1210 when, for exampe, SINE is maximum, COSINE is still showing few millivolts differentially, and a sinusodial voltage is present in COS/COSLO pins, here you can see the effect, from top to bottom, excittion (4 Vrms), IC COS input differential, IC COS and COSLO inputs respect GND, IC SIN input differential, IC SIn and SINLO inputs respect GND) 
 
 Removing the connection between SINLO and COSLO gets rid of this effect. 
 
 May the connection between SINLO and COSLO causing the problem with the error flags? If so, how can i solve this issue? 
 
 Thanks in advance.

@skowalik · Accepted Answer

Can you please provide the part # so I can do some research? If the output is as I expect this becomes a simple exercise of a dual FDA configured as a single-ended to differential conversion stage. The optimum solution for you might be single ADA4940-2 which is in a 4mm x 4mm LFCSP plus four-(4) resistors that could probably be in 0201 case size. 
 Sean)

@skowalik · Answer

manuslet, 
 This sounds suspiciously like you are using a synchro as your sensor. Can you please share the part # for the sensor so that I can do a bit of research to confirm. 
 If this is the case you can use a Scott-T transformer to convert the 3-Phase output of the sensor into a 2-Phase quadrature signal you'll need to drive the AD2S1210 and that should eliminate your problem assuming you adhere to the input parametric specifications in the datasheet. 
 Sean

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AD2S1210 input signal conditioning for 5 wire resolver