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13
PRODUCT SPECIFICATION
RC4200
Appendix 1—System Errors
There are four types of accuracy errors which affect overall
system performance. They are:
Nonimearity—Incremental deviation from absolute
accuracy. See Note 1.
Scaling Error—Linear deviation from absolute accuracy.
Output Offset—Constant deviation from absolute
accuracy.
Feedthrough.—Cross-product errors caused by input
offsets and external circuit limitations. See Note 2.
This nonlinearity error in the transfer function of the
RC4200 is
±
0.1% maximum (
±
0.03 maximum for the
RC4200A). That is,
The other system errors are caused by voltage offsets on the
inputs of the RC4200 and can be as high as
±
3.0% (
±
2.0%
for RC4200A).
Figure 12.
Notes:
1. The input circuits tend to become unstable at
I
1
, I
2
, I
4
< 50
m
A and linearity decreases when I
1
, I
2
, I
4
>
250
m
A (e.g., @ I
1
= I
2
= 500
m
A nonlinearity error
0.5%).
2. This section will not deal with feedthrough which is
proportional to frequency of operation and caused by stray
capacitance and/or bandwidth limitations. (refer to
Figure 12.)
3. Not including resistor tolerance or output offset on the
operational amplifier.
4. For 50
m
A
£
I
1
, I
2
, I
4
£
250
m
A.
I
3
I
I
I
4
--------- 0.1% F.S.
4
( )
=
V
0
V
V
Y
V
Z
---------------
R
R
R
1
R
2
------------- 3.0% F.S.
3
( )
( )
=
65-1871
RC4200
Multiplier
V
V
S
X
Y
O
S
R
1
R
2
-V
I
3
R
V
+V
3
6
4
5
8
7
1
2
I
2
I
1
I
4
V
Z
R
4
Ideal Op-Amp
V = 0
O
Errors Caused by Input Offsets
System errors can be greatly reduced by externally trimming
the input offset voltages of the RC4200. (
±
3.0% F.S. for
RC4200 and
±
0.1% for RC4200A.)
If X
OS
= X
OSX
, Y
OS
= Y
OSY
, Z
OS
= -V
OSZ
,
Figure 13. RC4200 with Input Offset Adjustment
Extended Range Circuit Errors
The extended range configurations have a disadvantage in
that additional accuracy errors may be introduced by resistor
product mismatching.
Multiplier
An error in resistor product matching will cause an
equivalent feedthrough or output offset error. See Figure 6.
R
1
R
b
= R
CX
R
d
±a
, V
X
feedthrough (V
Y
= 0) = I
a
V
X
R
2
R
a
= R
CY
R
d
±b,
V
Y
feedthrough (V
X
= 0) =
±b
V
Y
R
a
R
b
= R
C
R
d
±g
, V
0
offset (V
X
= V
Y
= 0) =
±g
V
REF
*
Note:
*
Output offset errors can always be trimmed out with the
output op amp offset adjust, VOS (R16).
V0 =
VY Feedthrough
VX Feedthrough
Scaling Error
Output Offset Error
VYVOSX
±
VXVOSY
±
V0VOSZ
±
VOSXVOSY
±
R0R4
R0R4
VXVY
VZ
1
VZ
65-1870
RC4200
Multiplier
V
V
S
X
Y
O
R
1
R
2
-V
R
V
3
6
4
5
8
7
1
2
V
Z
R
4
Ideal Op-Amp
V = 0
O
R
1
R
2
S
+V
S
-V
S
+V
S
-V
+V
S
S
-V
100 R
4
Z
OS
X
OS
then V
O
V
V
Y
V
Z
---------------
R
R
4
R
1
R
2
-------------
±
0.3% F.S.
3
( )