AD9774EB datasheet(19/24 Pages) AD

19 / 24 page

AD9774

–19–

REV. B

A multitone test vector may consist of several equal amplitude,

spaced carriers each representative of a channel within a defined

bandwidth as shown in Figure 42a. In many cases, one or more

tones are removed so the intermodulation distortion performance

of the DAC can be evaluated. Nonlinearities associated with the

DAC will create spurious tones of which some may fall back into

the “empty” channel thus limiting a channel’s carrier-to-noise

ratio. Other spurious components falling outside the band of

interest may also be important, depending on the system’s spectral

mask and filtering requirements.

This particular test vector was centered around one-half the

Nyquist bandwidth (i.e., fCLOCK/4) with a passband of fCLOCK/16.

Centering the tones at a much lower region (i.e., fCLOCK/10)

would lead to an improvement in performance while centering

the tones at a higher region (i.e., fCLOCK/2.5) would result in a

degradation in performance. Figure 43a shows the SFDR vs.

amplitude at 32 MSPS up to the Nyquist frequency while Fig-

ure 43b shows the SFDR vs. amplitude within the passband of

the test vector. In assessing a DAC’s multitone performance, it

is also recommended that several units be tested under exactly

the same conditions to determine any performance variability.

AD9774 EVALUATION BOARD

General Description

The AD9774-EB is an evaluation board for the AD9774 14-bit

DAC converter. Careful attention to layout and circuit design,

combined with a prototyping area, allows the user to easily and

effectively evaluate the AD9774 in signal reconstruction applica-

tions, where high resolution, high speed conversion is required.

This board allows the user the flexibility to operate the AD9774

in various configurations. The digital inputs are designed to be

driven directly from various word generators with the onboard

option to add a resistor network for proper load termination.

Provisions are also made to operate the AD9774 with either the

internal or external reference or to exercise the SLEEP or

SNOOZE power-savings feature.

AOUT – dBFS

–18

–16

–14

–12

–10

–8

–6

–4

–2

Figure 43a. Multitone SFDR vs. AOUT @ 32 MSPS

(Up to Nyquist)

AOUT – dBFS

–18

–16

–14

–12

–10

–8

–6

–4

–2

8MSPS

16MSPS

32MSPS

Figure 43b. Multitone SFDR vs. AOUT @ 32 MSPS

(Within Multitone Passband)

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