AD9280ARS Просмотр технического описания (PDF) - Analog Devices
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AD9280ARS Datasheet PDF : 24 Pages
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AD9280
0
–3
–6
–9
–12
–15
–18
–21
–24
1.0E+6
1.0E+7
1.0E+8
FREQUENCY – Hz
Figure 13. Full Power Bandwidth
1.0E+9
50
40
30
20
REFBS = 0.5V
10
REFTS = 2.5V
CLOCK = 32MHz
0
–10
–20
–30
–40
–50
0
0.5
1.0
1.5
2.0
2.5
3.0
INPUT VOLTAGE – V
Figure 14. Input Bias Current vs. Input Voltage
APPLYING THE AD9280
THEORY OF OPERATION
The AD9280 implements a pipelined multistage architecture to
achieve high sample rate with low power. The AD9280 distrib-
utes the conversion over several smaller A/D subblocks, refining
the conversion with progressively higher accuracy as it passes
the results from stage to stage. As a consequence of the distrib-
uted conversion, the AD9280 requires a small fraction of the
256 comparators used in a traditional flash type A/D. A sample-
and-hold function within each of the stages permits the first
stage to operate on a new input sample while the second, third
and fourth stages operate on the three preceding samples.
OPERATIONAL MODES
The AD9280 is designed to allow optimal performance in a
wide variety of imaging, communications and instrumentation
applications, including pin compatibility with the AD876-8 A/D.
To realize this flexibility, internal switches on the AD9280 are
used to reconfigure the circuit into different modes. These modes
are selected by appropriate pin strapping. There are three parts
of the circuit affected by this modality: the voltage reference, the
reference buffer, and the analog input. The nature of the appli-
cation will determine which mode is appropriate: the descrip-
tions in the following sections, as well as Table I should assist in
selecting the desired mode.
Table I. Mode Selection
Modes
Input
Connect
Input MODE REFSENSE
Span Pin
Pin
REF
REFTS REFBS Figure
TOP/BOTTOM AIN
AIN
1V
AVDD Short REFSENSE, REFTS and VREF Together
AGND 18
2V
AVDD AGND
Short REFTS and VREF Together AGND 19
CENTER SPAN AIN
AIN
1V
AVDD/2 Short VREF and REFSENSE Together AVDD/2 AVDD/2 20
2V
AVDD/2 AGND
No Connect
AVDD/2 AVDD/2
Differential
AIN Is Input 1 1 V
REFTS and
REFBS Are
Shorted Together
for Input 2
2V
AVDD/2 Short VREF and REFSENSE Together AVDD/2 AVDD/2 29
AVDD/2 AGND
No Connect
AVDD/2 AVDD/2
External Ref
AIN
AD876-8
AIN
2 V max AVDD AVDD
AGND
2V
Float or AVDD
AVSS
No Connect
No Connect
Span = REFTS
21, 22
– REFBS (2 V max)
Short to Short to 23
VREFTF VREFBF
Short to Short to 30
VREFTF VREFBF
–8–
REV. E
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