Document created by analog-archivist on Feb 23, 2016
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Q

I have a query about the Comment Mode Voltage of SIN/COS input in our AD2S12XX
for the AD2S1200, CMV description:Common Mode Volts 100 mV Peak CMV @ SinLO,
CosLO, with respect to REFOUT @ 10 kHz
For the AD2S1205, CMV description: Common-Mode Voltage
100
mV peak
CMV with respect to REFOUT/2 at 10 kHz

as the SIN/COS input VP-P is 2.3V~4V  with AD2S1200 and AD2S1205,and  the
voltages Sin, SinLO, Cos, and CosLO relative to AGND must always be between 0.2
V and AVDD.so  the CMV would  be above the 4/2=2V, right? How to understand the
100 mVpeak.
Or  we try to understand the CMV as the SIN pin or COS pin absolute input
value ,and the 100 mv is the offset value which respect to REFOUT , while, why
the respect value is REFOUT in AD2S1200 and is REFOUT/2  in AD2S1205?
I was a little puzzle about it ,could you help to clarify ? thanks a lot!

A

The specification means that the part will set up a common mode on the inputs
signals with a resolver connected with no external circuitry between the
resolver and the AD2S1205 which will be within 100mV of the Refout/2 voltage
The AD2S1200 spec should also say Refout/2.

For the AD2S1210 the common mode would also be REFOUT/2. It was removed from
the spec table in the AD2S1210 but is referred to later on in the data sheet on
page 19.
“In this recommended configuration, the converter introduces a VREF/2 offset in
the SIN, SINLO, COS, and COSLO signal outputs from the resolver.”

For a max 4Vpk-pk differential signal this would be split 50:50 between Sin and
SinLo. That gives a 2V pk-pk signal per input. With a 1.25V common mode that
gives a range of 0.25V to 2.25V.