ADC912A View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADC912A Datasheet PDF : 16 Pages
| |||
ADC912A
BIPOLAR ANALOG INPUT OPERATION
Bipolar analog input operation is achieved with an external
amplifier providing an analog offset. Figures 17 and 18 show
two circuit topologies that result in different digital-output cod-
ing. In Figure 17, offset binary coding is produced when the
external amplifier is connected in the inverting mode. Figure 19
shows the ideal transfer characteristics for both the inverting
and noninverting configurations given in Figures 17 and 18.
؎VIN
R3
RFS
A1
R4
1
AIN
R2
RZ
ADC912A*
R1
–5V
2
VREFIN
0.1F 10F
3
AGND
R1 = R2 = 20k⍀
SEE TABLE II FOR VALUES OF R3, R4, RZ, AND RFS
A1: OP27 LOWEST NOISE, OP42 BEST BANDWIDTH
*EXTRA PINS OMITTED FOR CLARITY
Figure 17. Noninverting Bipolar Analog Input Operation
The scaling resistors chosen in bipolar input applications should
be from the same manufacturer to obtain good resistor tracking
performance over temperature. When potentiometers are used
for absolute adjustment, 0.1% tolerance resistors should still be
used as shown in Figures 17 and 18 to minimize temperature
coefficient errors.
؎VIN
RFS R1
RZ
R3
–5V
R2
1
A1
AIN
ADC912A*
2 VREFIN
0.1F 10F
+
3 AGND
SEE TABLE III FOR VALUES OF R1, R2, R3, R4, RZ, AND RFS
A1: OP27 LOWEST NOISE, OP42 BEST BANDWIDTH
*EXTRA PINS OMITTED FOR CLARITY
Figure 18. Inverting Bipolar Analog Input
Calibration of the bipolar analog input circuits (Figures 17 and
18) should begin with zero adjustment first. Apply a +1/2 LSB
analog input to AIN, (see Tables II and III) and adjust RZ until the
successive digital output codes flicker between the following codes:
For noninverting, Figure 17 1000 0000 0000
1000 0000 0001
For inverting, Figure 18
0111 1111 1111
0111 1111 1110
Next, adjust full scale by applying a FS–3/2 LSB analog input to
AIN, (see Tables II and III) and adjust RFS until the successive
digital output codes flicker between the following codes:
For Noninverting, Figure 17 1111 1111 1110
1111 1111 1111
For Inverting, Figure 18
0000 0000 0001
0000 0000 0000
Table II. Resistor and Potentiometer Values Required for
Figure 17
VIN Range R3 R4 RZ RFS
V
k⍀ k⍀ k⍀ k⍀
± 2.5
± 5.0
± 10.0
0 40.2 0.5 0.5
20.0 19.8 0.5 1.0
29.8 10.0 0.5 0.5
1/2 LSB
mV
0.61
1.22
2.44
FS/2–3/2 LSB
V
2.49817
4.99634
9.99268
Table III. Resistor and Potentiometer Values Required for
Figure 18
VIN Range R1 R2 R3 RZ
V
k⍀ k⍀ k⍀ k⍀
± 2.5
± 5.0
± 10.0
20.0 41.2 40.2 2
20.0 20.5 20.0 1
20.0 10.5 10.2 0.5
RFS 1/2 LSB FS/2–3/2 LSB
k⍀ mV
V
1 0.61
1 1.22
1 2.44
2.49817
4.99634
9.99268
DIGITAL OUTPUT
111...111
111...110
100...001
100...000
011...111
011...110
INVERTING
FIGURE 18
NON-
INVERTING
FIGURE 17
+
FS
2
– 1LSB
000...001
000...000
–
FS
2
0V
VIN – Input Voltage
+
FS
2
Figure 19. Ideal Input/Output Transfer Characteristics for
Bipolar Input Circuits
–10–
REV. B
|
|
Share Link: 