AD9480 データシートの表示（PDF） - Analog Devices
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AD9480 Datasheet PDF : 28 Pages
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The AD9480 can be easily configured for different full-scale
ranges. See the Voltage Reference section for more information.
Optimal performance is achieved with a 1 V p-p analog input.
SENSE = GND
VIN+
500mV 2.0V
VIN–
DIGITALOUT = ALL 1s
2.0V
DIGITALOUT = ALL 0s
Figure 33. Analog Input Full Scale
VOLTAGE REFERENCE
A stable and accurate 1.0 V reference is built into the AD9480.
Users can choose this internal reference or provide an external
reference for greater accuracy and flexibility. Figure 35 shows
the typical reference variation with temperature. Table 9
summarizes the available reference configurations.
VIN+
VIN–
ADC
CORE
AD9480
Fixed Reference
The internal reference can be configured for a differential span
of 1 V p-p (see Figure 37). It is recommended to place a 0.1 µF
capacitor as close as possible to the VREF pin; a 10 µF capacitor
is also required (see the PCB layout for guidance). If the
internal reference of the AD9480 is used to drive multiple
converters to improve gain matching, the loading of the
reference by the other converters must be considered. Figure 37
depicts how the internal reference voltage is affected by loading.
1.0085
1.0080
1.0075
1.0070
1.0065
1.0060
1.0055
1.0050
1.0045
1.0040
1.0035
–40
–20
0
20
40
60
80
TEMPERATURE (°C)
Figure 35. Typical Reference Variation with Temperature
10µF 0.1µF
VREF
SENSE
VREF
+
10µF 0.1µF
SENSE
7kΩ
SELECT
LOGIC
Figure 36. Internal Fixed Reference (1 V p-p)
0
–0.1
–0.2
7kΩ
0.5V
Figure 34. Internal Reference Equivalent Circuit
Table 9. Reference Configurations
SENSE Voltage
Resulting VREF
AVDD
N/A (External Reference Input)
0.5 V (Self-Biased)
0.5 × (1 + R1/R2) V
AGND to 0.2 V
1.0 V
–0.3
–0.4
–0.5
0
Reference
External
Programmable
Internal Fixed
0.5
1.0
1.5
2.0
2.5
3.0
IREF (mA)
Figure 37. Internal VREF vs. Load Current
Differential Span
1 × External Reference Voltage
1 × VREF (0.75 V p-p to 1.5 V p-p)
1 V p-p
Rev. A | Page 17 of 28
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