AD9240ASRL datasheet(11/24 Pages) AD

11 / 24 page

AD9240

REV.

–11–

Table I. Analog Input Configuration Summary

Input

Input Range (V)

Figure

Connection

Coupling

Span (V)

VINA

VINB

Comments

Single-Ended

0 to 2

32, 33

Best for stepped input response applications, suboptimum THD

and noise performance, requires

±5 V op amp.

× VREF

0 to

VREF

32, 33

Same as above but with improved noise performance due to

× VREF

increase in dynamic range. Headroom/settling time requirements

±5 V op amp should be evaluated.

0 to 5

2.5

32, 33

Optimum noise performance, excellent THD performance. Requires

op amp with VCC > +5 V due to insufficient headroom @ 5 V.

× VREF

2.5 – VREF

2.5

Optimum THD performance with VREF = 1, noise performance

improves while THD performance degrades as VREF increases

2.5 + VREF

to 2.5 V. Single supply operation (i.e., +5 V) for many op amps.

Single-Ended

2 or

0 to 1 or

1 or VREF

Suboptimum ac performance due to input common-mode level

× VREF

0 to 2

× VREF

not biased at optimum midsupply level (i.e., 2.5 V).

0 to 5

2.5

Optimum noise performance, excellent THD performance.

× VREF

2.5 – VREF

2.5

Flexible input range, Optimum THD performance with VREF = 1.

Noise performance improves while THD performance degrades as

2.5 + VREF

VREF increases to 2.5 V.

Differential

AC or

2 to 3

3 to 2

29–31

Optimum full-scale THD and SFDR performance well beyond the

A/Ds Nyquist frequency.

× VREF

2.5 – VREF/2

2.5 + VREF/2

29–31

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

2.5 + VREF/2

2.5 – VREF/2

performance.

1.25 to 3.75

3.75 to 1.25

29–31

Widest dynamic range (i.e., ENOBs) due to optimum noise

performance.

1VINA 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

INTERNAL

SENSE

VREF

INTERNAL

2.5

SENSE

REFCOM

INTERNAL

≤ SPAN ≤ 5 AND

≤ VREF ≤ 2.5 AND

VREF AND SENSE

SPAN = 2

× VREF

VREF = (1 + R1/R2)

SENSE AND REFCOM

EXTERNAL

≤ SPAN ≤ 51 ≤ VREF ≤ 2.5

SENSE

AVDD

(NONDYNAMIC)

VREF

EXT. REF.

EXTERNAL

≤ SPAN ≤ 5

CAPT and CAPB

SENSE

AVDD

(DYNAMIC)

Externally Driven

VREF

REFCOM

EXT. REF. 1

CAPT

EXT. REF. 2

CAPB

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