What function of "segment switcher", "Quadrant selector", "octant selector" blocks in R2D converters?
Why we couldn't just connect sine and cosine signals from resolver to the multiplying DACs?
The segment switching block simplifies and improves the operation in the next block. For example with a quadrant selector..
The first 2 MSBs of the output angle (phi) would control the segment switcher. Segment switching enables selection of the quadrant in which the input angle (theta) lies and sets the polarities of the inputs, sin(theta) & cos(theta) , to the next stage. The next stage is a multiplying subtractor block where the output is sin(theta)cos(phi) - cos(theta)sin(phi) = sin(theta - phi). Because of the segment switcher stage this block needs only to operate in one quadrant making the system more accurate as the fullscale range is only one quadrant.
Can you indicate which part in particular you are referring to? This will help us to deal with your question more efficiently.
ADI's RDC portfolio is listed on the following web page
The more modern parts are the AD2S1200, AD2S1205 and AD2S1210. For these parts you can directly connect the resolver sine and cosine signals to the device as the AD2S12xx parts provide a bias signal and compensate for any phase shift up to a +/-44 degree limit in the case of the AD2S1205 and AD2S1210.
I'm talking about part in red square (in attachment).
At first, on the quadrant selector input we have modulated signals - sin(theta)*sin(wt) and cos(theta)*sin(wt), where sin(wt) is the excitation.
What function quadrant selector switch - sin(theta) or sin(wt)?
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