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I have a question about AD2S1200 sin/cos input. The datasheet says that, voltage swing is 3.6Vpp typically, but the common mode volts is 100mV, respect to Refout. Does it mean the common mode voltage should be Refout+/-0.1V? But I also find another description in datasheet where it says the converter introduce a Vref/2 offset in the sin/cos signal. So I am confused that whether the offset should be Vref/2 or Vref, and is that offset generated by AD2S1200 internally or we need to introduce a offset externally in the input signal. Also, if I find the sin/cos signal(Vpp) from resolver is smaller than the requirement of 3.6Vpp, what should I do to amplify the input signal. May I could try to use a large Exc signal by changing the gain of buffer circuit?
The Common mode Volts spec should be with respect to Refout/2. The AD2S1200 internally generates the bias that will centre the input differential signals on refout/2. The customer can overdrive this is desired, in which case they should ensure that the inputs are at all times between 0.2V and Vdd [see Note 1.] If the inputs are too small the best option is to increase the gain on the excitation buffer amp. This is the simplest and should introduce no additional error. Another option is to introduce gain on both the Sine and Cosine differential signals. However this is twice the effort and can introduce amplitude mismatch between the Sine and Cosine if proper care is not taken.