Datasheet

REV. E
AD9221/AD9223/AD9220
–13–
Table I. Analog Input Configuration Summary
Input Input
Input Range (V)
Figure
Connection Coupling Span (V) VINA* VINB* No. Comments
Single-Ended DC 2 0 to 2 1 13, 14 Best for stepped input response applica-
tions, suboptimum THD, and noise
performance. Requires ±5 V op amp.
2 × VREF 0 to VREF 13, 14 Same as above but with improved noise
2 × VREF performance due to increase in dynamic
range. Headroom/settling time require-
ments of ±5 V op amp should be evaluated.
50 to 5 2.5 13, 14 Optimum noise performance, excellent
THD performance. Requires op amp with
VCC > 5 V due to headroom issue.
2 × VREF 2.5 – VREF 2.5 24 Optimum THD performance with VREF =
to 1. Noise to performance improves while
2.5 + VREF 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 0 to 1 or 1 or VREF 15 Suboptimum ac performance due to input
2 × VREF 0 to 2 × VREF common-mode level not biased at optimum
midsupply level (i.e., 2.5 V).
50 to 5 2.5 15 Optimum noise performance, excellent THD
performance, ability to use ±5 V op amp.
2 × VREF 2.5 – VREF 2.5 16 Flexible input range, optimum THD
to performance with VREF = 1. Noise
2.5 + VREF 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 AC 2 2 to 3 3 to 2 19 Optimum full-scale THD and SFDR
(via Transformer) performance well beyond the A/D’s Nyquist
frequency. Preferred mode for under-
sampling applications.
2 × VREF 2.5 – VREF/2 2.5 + VREF/2 19 Same as 2 V to 3 V input range with the
to to exception that full-scale THD and SFDR
2.5 + VREF/2 2.5 – VREF/2 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 19 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.
*VINA and VINB can be interchanged if signal inversion is required.