Datasheet
AD9225
–11–
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 8, 9 Best for stepped input response applications;
requires ±5 V op amp.
2 ¥ VREF 0 to VREF 8, 9 Same as above but with improved noise
2 ¥ VREF performance due to increase in dynamic
range. Headroom/settling time requirements
of ±5 V op amp should be evaluated.
40 to 4 2.0 8, 9 Optimum noise performance, excellent THD
performance, often requires low distortion op
amp with VCC > +5 V due to its headroom
issues.
2 ¥ VREF 2.0 – VREF 2.0 21 Optimum THD performance with VREF = 1.
to Single-supply operation (i.e., +5 V) for many
2.0 + VREF op amps.
Single-Ended AC 2 or 0 to 1 or 1 or VREF 10, 11
2 ¥ VREF 0 to 2 ¥ VREF
4 0.5 to 4.5 2.0 11 Optimum noise performance, excellent THD
performance; ability to use ±5 V op amp.
2 ¥ VREF 2.0 – VREF 2.0 10 Flexible input range, optimum THD perfor-
to mance with VREF = 1. Ability to use either
2.0 + VREF +5 V or ±5 V op amp.
Differential AC/DC 2 2 to 3 3 to 2 12, 13 Optimum full-scale THD and SFDR perfor-
(via Transformer) mance well beyond the ADC’s Nyquist
or Amplifier frequency. Preferred mode for under-
sampling applications.
2 ¥ VREF 2.0 – VREF/2 2.0 + VREF/2 12, 13 Same as above with the exception that full-
to to scale THD and SFDR performance can be
2.0 + VREF/2 2.0 – VREF/2 traded off for better noise performance.
4.0 1.5 to 3.5 3.5 to 1.5 12, 13 Optimum noise performance.
*VINA and VINB can be interchanged if signal inversion is required.
Table II. Reference Configuration Summary
Reference Input Span (VINA–VINB)
Operating Mode (V p-p) Required VREF (V) Connect To
Internal 2 1 SENSE VREF
Internal 4 2 SENSE REFCOM
Internal 2 £ SPAN £ 4 and 1 £ VREF £ 2.0 and R1 VREF and SENSE
SPAN = 2 ⫻ VREF VREF = (1 + R1/R2) R2 SENSE and REFCOM
External 2 £ SPAN £ 41 £ VREF £ 2.0 SENSE AVDD
(Nondynamic) VREF External Reference
External 2 £ SPAN £ 4 CAPT and CAPB SENSE AVDD
(Dynamic) Externally Driven VREF AVSS
External Reference CAPT
External Reference CAPB
Rev. C