AD2S1205

Rev. A | Page 8 of 20

RESOLVER FORMAT SIGNALS

(A) CLASSICAL RESOLVER

S1

S3

S2

S4

R1

R2

θ

(B) VARIABLE RELUCTANCE RESOLVER

S1

S3

S2

S4

R1

R2

θ

Figure 3. Classical Resolver vs. Variable Reluctance Resolver

A classical resolver is a rotating transformer that typically has a

primary winding on the rotor and two secondary windings on

the stator. A variable reluctance resolver, on the other hand, has the

primary and secondary windings on the stator and no windings

on the rotor, as shown in Figure 3; however, the saliency in this

rotor design provides the sinusoidal variation in the secondary

coupling with the angular position. For both designs, the resolver

output voltages (S3 − S1, S2 − S4) are as follows:

Sinθ

t

Sin

E

S1

S3

0

×

ω

=

−

)

(

(1)

Cosθ

t

Sin

E

S4

S2

0

×

ω

=

−

)

(

where:

θ is the shaft angle.

Sin(ωt) is the rotor excitation frequency.

The stator windings are displaced mechanically by 90° (see

Figure 3). The primary winding is excited with an ac reference.

The amplitude of subsequent coupling onto the secondary

windings is a function of the position of the rotor (shaft)

relative to the stator. The resolver therefore produces two

output voltages (S3 − S1, S2 − S4), modulated by the sine and

cosine of the shaft angle. Resolver format signals refer to the

signals derived from the output of a resolver, as shown in

Equation 1. Figure 4 illustrates the output format.

0°

S2 – S4

(COSINE)

S3 – S1

(SINE)

R2 – R4

(REFERENCE)

90°

180°

θ

270°

360°

Figure 4. Electrical Resolver Representation