Datasheet
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)
CS
1
CS
2
CS
3
CS
4
A0
A1
SCLK
DATA
V
DD
V
SS
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)
u IN
VEL OUT
u OUT
Figure 17. AD2S90 Transfer Function
The open-loop transfer function is given by:
θ
OUT
θ
IN
=
K
1
K
2
s
2
(1 + st
1
)
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:
KKK
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
1k100
FREQUENCY – Hz
10k
Figure 18. AD2S90 Gain Plot
FREQUENCY – Hz
0
–180
10k
–140
–160
101
–120
–100
–80
–60
–40
–20
1k100
Figure 19. AD2S90 Phase Plot