### Q

We want to have an error due to Phase shift of less then 1 lsb with theseparameters: RotationRate=6000rpm ReferenceFrequency=10Khz. What is the maximun

phase shift that can be tolerated between the reference excitation and the

sin/cos signals.

### A

The Error you are referring to is caused by the rotation of the resolver.Basically at high rotation rates the resolver starts to act like an electric

motor and produces speed voltages. This are in quadrature to the main signal

and result in an additional error through the RDC.

The formula to calculate this error is on page 17 of the datasheet:

Error = Phase shift x [rotation rate / reference frequency]

The main factor in the formula is the Phase shift, which is the phase shift

between the reference signal and the Sin/Cos inputs. This phase shift is

primarily caused by the resolver itself i.e. resistance of the rotor coil

causes a phase shift from what is applied to the rotor to what is then

generated across the stators.

The AD2S1200 internally generates a synthetic reference to compensate for this

phase shift. It can reduce a phase shift of +/-45 degrees down to 10 degrees.

However for you this is not quite enough as he would then have the following

with the speed and freq conditions he outlined :

Error = 10 degrees x [100rps / 10kHz]

= 0.1 degrees = 6 arc min

One lsb = 5.3 arc min.

The reduce this error still further you need to further reduce the phase shift

between the

reference and the Sin/Cos signals. So after all that explanation the answer to

your

questions is:

Error = Phase shift x [rotation rate / reference frequency]

=> Phase shift = Error x [reference freq / rotation rate]

= [0.088 degrees] x [10,000/100]

= 8.83 degrees.

i.e. You need to keep the phase shift below 8.8 degrees to be able to keep the

additional error below 1 lsb [5.3 arc min.]