AD9221/AD9223/AD9220
Table I. Analog Input Configuration Summary
Input
Connection
Single-Ended
Input
Coupling Span (V)
Input Range (V)
Figure
#
VINA1
VINB1
Comments
DC
2
0 to 2
1
39, 40
Best for stepped input response applications, suboptimum
THD and noise performance, requires ±5 V op amp.
2 × VREF
0 to
2 × VREF
VREF
39, 40
Same as above but with improved noise performance due to
increase in dynamic range. Headroom/settling time require-
ments of ±5 V op amp should be evaluated.
5
0 to 5
2.5
2.5
39, 40
50
Optimum noise performance, excellent THD performance,
Requires op amp with VCC > +5 V due to headroom issue.
2 × VREF
2.5 – VREF
to
2.5 + VREF
Optimum THD performance with VREF = 1, noise
performance improves while THD performance degrades as
VREF increases to 2.5 V. Single supply operation (i.e., +5 V) for
many op amps.
Single-Ended
AC
2 or
2 × VREF
0 to 1 or
0 to 2 × VREF
1 or VREF
2.5
41
41
42
Suboptimum ac performance due to input common-mode
level not biased at optimum midsupply level (i.e., 2.5 V).
5
0 to 5
Optimum noise performance, excellent THD performance,
ability to use ±5 V op amp.
2 × VREF
2.5 – VREF
to
2.5 + VREF
2.5
Flexible input range, Optimum THD performance with
VREF = 1. Noise performance improves while THD perfor-
mance degrades as VREF increases to 2.5 V. Ability to use
+5 V or ±5 V op amp.
Differential
(via Transformer)
AC
2
2 to 3
3 to 2
45
Optimum full-scale THD and SFDR performance well be-
yond the A/Ds Nyquist frequency. Preferred mode for under-
sampling applications.
2 × VREF
2.5 – VREF/2 2.5 + VREF/2 45
to to
2.5 + VREF/2 2.5 – VREF/2
Same as 2 V to 3 V input range with the exception that full-scale
THD and SFDR performance can be traded off for better noise
performance. Refer to discussion in AC Coupling and Interface
Issue section and Simple AC Interface section.
5
1.75 to 3.25
3.25 to 1.75
45
Optimum Noise performance. Also, the optimum THD and
SFDR performance for “less than” full-scale signals (i.e.,
–6 dBFS). Refer to discussion in AC Coupling and Interface
Issue section and Simple AC Interface section.
NOTE
1VINA and VINB can be interchanged if signal inversion is required.
Table II. Reference Configuration Summary
Input Span (VINA–VINB)
Reference
Operating Mode
(V p-p)
Required VREF (V)
Connect
To
INTERNAL
INTERNAL
INTERNAL
2
5
1
2.5
SENSE
SENSE
R1
VREF
REFCOM
VREF AND SENSE
SENSE AND REFCOM
2 ≤ SPAN ≤ 5 AND
SPAN = 2 × VREF
1 ≤ VREF ≤ 2.5 AND
VREF = (1 + R1/R2)
R2
EXTERNAL
(NONDYNAMIC)
2 ≤ SPAN ≤ 5
1 ≤ VREF ≤ 2.5
SENSE
VREF
AVDD
EXT. REF.
EXTERNAL
(DYNAMIC)
2 ≤ SPAN ≤ 5
CAPT and CAPB
Externally Driven
SENSE
VREF
EXT. REF.
EXT. REF.
AVDD
REFCOM
CAPT
CAPB
–13–
REV. D
ADI [ ADI ]
