adc1225ccd-1 National Semiconductor Corporation, adc1225ccd-1 Datasheet - Page 14

• Manufacturer Part Number: adc1225ccd-1
• Description: 12-bit Plus Sign Mp Compatible A/d Converters
• Manufacturer: National Semiconductor Corporation

Functional Description
A simpler although slightly less accurate approach is to
ground V
output Error will be well under
done so that the potentiometer is ‘‘centered’’ within the
0 000 000 range A positive voltage at the V
reduce the output code The adjustment range is
7 2 POSITIVE AND NEGATIVE FULL-SCALE
Unipolar Inputs
Apply a differential input voltage which is 1 5 LSB below the
desired analog full-scale voltage (V
Typical Applications
b
30 LSB
Input must have some
current return path to
signal ground
ADJUSTMENT
IN(
a
FIGURE 15 Zero Adjust Circuit
)
and V
IN(
b
)
and adjust for all zeros at the
LSB if the adjustment is
F
) and adjust the magni-
(Continued)
OS
TL H 5676 – 11
input will
a
4 to
14
tude of the V
ing from 0 1111 1111 1110 to 0 1111 1111 1111
Bipolar Inputs
Do the same procedure outlined above for the unipolar case
and then change the differential input voltage so that the
digital output code is just changing from 1 0000 0000 0001
to 1 0000 0000 0000 Record the differential input voltage
V
should be
Calculate the difference between Vx and the ideal voltage
Then apply a differential input voltage of
and adjust the magnitude of V
code
1 0000 0000 0000 That will obtain the positive and negative
full-scale transition with symmetrical minimum error
X
D


b
V
the ideal differential input voltage for that transition
e
X
V
V
b
is
F
X
a
D
2
b
J
just
8192
REF
V

F
b
input so that the output code is just chang-
V
J
changing
F
a
8192
V
F
J
from
REF
TL H 5676 – 12
1 0000 0000 0001
so the digital output
to