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Application Note
AN115
A Compendium of Application Circuits
for Xicor’s Digitally-Controlled (XDCP) Potentiometers
Chuck Wojslaw (March 1998)
Introduction
This Note lists a number of application circuits for Xicor’s
digitally-controlled (XDCP) potentiometers. The applica-
tion circuits, shown in basic form, illustrate the wide variety
of possible functions that can be implemented using the
variability of the potentiometer in conjunction with stan-
dard active devices like operational amplifiers and com-
parators. The types of circuits include control circuits,
converters, filters, signal processing circuits, regulators,
waveshapers, analog computing circuits, and signal
sources. In the detail design of these circuits, proper sup-
ply filtering and proper grounding techniques must be
used.
Electronic Digitally-controlled (XDCP) potentiometers
provide three powerful application advantages; (1) the
variability and reliability of a solid-state potentiometer, (2)
the flexibility of computer-based digital controls, and (3)
the retentivity of nonvolatile memory used for the storage
of multiple potentiometer settings or data. In addition, the
packages of the potentiometers are completely
compatible with other electronic components and hence
reduce manufacturing assembly costs.
Expanded versions of many of the circuits listed in this
paper are available in other Xicor application notes. The
reader is invited to examine the Application Note Index for
these cases.
Xicor’s potentiometers are controlled through the 2-wire,
3-wire, or SPI computer serial-interfaces or buses. For
front panel, pushbutton type applications, Xicor’s pushpots
are recommended. General technical publications and
other Xicor application notes discuss the various computer
serial-interfaces to the electronic potentiometer.
Applications
V
R
V
R
V
W
I
Three terminal Potentiometer;
Variable voltage divider
Two terminal Variable Resistor;
Variable current
Figure 1. Basic Configurations of Electronic Potentiometers
AN115-1
Xicor Application Note
AN115
Application Circuits
Buffered Reference Voltage
Cascading Techniques
R
1
+
V
+
V
+V
+
5
V
V
W
+
OP-07
V
REF
X
V
OUT
V
W
–
–5V
+
V
V
OUT
= V
W
V
W
(a)
(b)
Noninverting Amplifier
Voltage Regulator
V
S
+
LM308A
–
V
O
V
IN
317
V
O
(REG)
R
1
R
2
I
adj
R
1
R
2
V
O
= (1+R
2
/R
1
)V
S
V
O
(REG) = 1.25V (1+R
2
/R
1
)+I
adj
R
2
Offset Voltage Adjustment
Comparator with Hysterisis
+5V
R
1
R
2
2.2K
W
LT311A
V
S
V
S
–
V
O
100K
W
+
–
V
O
+
TL072
10K
W
R
1
R
2
10K
W
10K
W
V
UL
= {R
1
/(R
1
+R
2
)} V
O
(max)
V
LL
= {R
1
/(R
1
+R
2
)} V
O
(min)
+12V
-12V
AN115-2
Xicor Application Note
AN115
Application Circuits
Attenuator
Filter
C
V
S
+
R
1
R
2
–
V
O
–
V
O
R
V
S
+
LT1097
R
3
R
2
R
4
R
1
= R
3
= R
4
R
1
R
2
= 2R
1
V
O
= G V
S
-1/2
£
G
£
+1/2
G
O
= 1 + R
2
/R
1
fc = 1/(2
p
RC)
Inverting Amplifier
Equivalent L-R Circuit
R
1
R
2
V
S
C
1
R
2
–
V
O
V
S
+
–
+
R
1
Z
IN
V
O
= G V
S
G = - R
2
/R
1
R
3
Z
IN
= R
2
+ s R
2
(R
1
+ R
3
) C
1
= R
2
+ s Leq
(R
1
+ R
3
) >> R
2
Function Generator
C
–
R
2
R
1
–
+
}
R
A
+
}
R
B
frequency
µ
R
1
, R
2
, C
amplitude
µ
R
A
, R
B
AN115-3
Xicor Application Note
AN115
Application Circuits
I to V Converter
Current Source
R
1
R
1
I
S
V
R
R
R
3
–
R
1
R
2
+
R
1
–
R
L
V
O
+
R
1
I
S
+
–
V
O
/ I
S
= -R
3
(1+R
2
/R
1
) + R
2
I
S
= V
R
/R
Phase Shifter
Capacitance Multiplier
R
1
R
1
R
1
R
2
V
S
–
+
–
V
O
–
+
+
C
C
R
C
in
C
IN
= C (1 + R
2
/R
1
)
V
O
/V
S
= 180° – 2tan
-1
w
RC
Absolute Value Amplifier with Gain
Level Detector
+
2R
V
S
V
S
R
1
R
R
R
R
1
R
2
–
V
OUT
–
–
+
V
O
+
+
+
A
1
A
2
V
R
V
O
= |V
S
|
R
1
R
V
OUT
= High for V
S
< – V
R
R
1
R
2
V
OUT
= Low for V
S
> – V
R
R
1
R
2
R
1
+ R
2
= R
POT
AN115-4
Xicor Application Note
AN115
Application Circuits
Level Detector
Oscillator
V
R
EFERENCE
(V
R
)
V
H
+
5
V
V
H
R
–
V
+
V
OUT
V
W
+
–
V
OUT
V–
+
V
L
V
W
R
2
V
L
+
C
+5V
V
TRANSDUCER
(V
T
)
R
3
R
1
–
V
T
>V
W
, V
OUT
=
High
Frequency
µ
R, C
µ
V
T
<V
W
, V
OUT
=
Low
Duty Cycle
R
1
, R
2
, R
3
Time Delay
+5
V
V
OUT
V
H
V
W
+
5
V
+5V
–
V
S
t
V
OUT
+
+5V
V
W
V
NI
t
V
L
V
NI
+5V
V
OUT
t
V
S
D
t
R
C
D
t = RC
ln
( )
5V
5V – V
W
AN115-5
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