AD2S90

REV. D

–9–

REMOTE MULTIPLE SENSOR INTERFACING

The DATA output of the AD2S90 is held in a high impedance

state until

CS is taken LO. This allows a user to operate the

AD2S90 in an application with more than one converter con-

nected on the same line. Figure 16 shows four resolvers inter-

faced to four AD2S90s. Excitation for the resolvers is provided

locally by an oscillator.

SCLK, DATA and two address lines are fed down low loss

cables suitable for communication links. The two address lines

are decoded locally into

CS for the individual converters. Data

is received and transmitted using transmitters and receivers.

2-4 DECODING

(74HC139)

A0

A1

SCLK

DATA

0V

AD2S90

1

RES1

AD2S90

2

RES2

AD2S90

3

RES3

AD2S90

4

RES4

4

4

4

4

2

2

OSC

BUFFER

Figure 16. Remote Sensor Interfacing

CIRCUIT DYNAMICS/ERROR SOURCES

Transfer Function

The AD2S90 operates as a Type 2 tracking servo loop. An

integrator and VCO/counter perform the two integrations inher-

ent in a Type 2 loop.

The overall system response of the AD2S90 is that of a unity

gain second order low-pass filter, with the angle of the resolver

as the input and the digital position data as the output. Figure

17 illustrates the AD2S90 system diagram.

A2 (S)

A1 (S)

IN

VEL OUT

OUT

Figure 17. AD2S90 Transfer Function

The open-loop transfer function is given by:

θ

OUT

θ

IN

=

s

2

(1

+ st

1

+ st

2

(5)

where:

As

K

s

st

st

1

11

2

1

1

()

=

+

+

tms

ts

1

2

10

90

=

=

.

µ

(6)

As

K

s

K

V

LSB

K

LSB V

2

2

1

2

4 875

614 400

()

./(

sec)

,

/(

sec)

=

=×

=×

(7)

The AD2S90 acceleration constant is given by:

KK

K

a

=×

≅

×

−

12

62

30 10

.

sec

(8)

The AD2S90’s design has been optimized with a critically

damped response. The closed-loop transfer function is given by:

θ

θ

OUT

IN

st

st

s

KK

st

KK

=

+

++

+

1

1

1

1

2

12

3

2

12

(9)

The normalized gain and phase diagrams are given in Figures 18

and 19.

5

–45

–30

–40

10

–35

1

–15

–25

–20

–10

–5

0

1k

100

FREQUENCY – Hz

10k

Figure 18. AD2S90 Gain Plot

FREQUENCY – Hz

0

–180

10k

–140

–160

10

1

–120

–100

–80

–60

–40

–20

1k

100

Figure 19. AD2S90 Phase Plot