AD9913 datasheet(13/32 Pages) AD

13 / 32 page

Data Sheet

AD9913

Rev. C | Page 13 of 32

AUXILIARY ACCUMULATOR

In addition to the phase accumulator of the DDS, the AD9913

has an auxiliary accumulator. This accumulator can be con-

figured to support either an automatic sweep of one of the

programmable characteristics of the DDS output (frequency or

phase), or it can be configured to implement a change in the

denominator of the frequency equation given in the DDS Core

section. For further details, refer to the Programmable Modulus

Mode section.

10-BIT DAC

The AD9913 incorporates an integrated 10-bit, current output

DAC. The output current is delivered as a balanced signal using

two outputs. The use of balanced outputs reduces the potential

amount of common-mode noise present at the DAC output,

offering the advantage of an increased signal-to-noise ratio. An

external resistor (RSET) connected between the RSET pin and

AGND establishes the reference current. The full-scale output

current of the DAC (IOUT) is produced as a scaled version of the

reference current. The recommended value of RSET is 4.62 kΩ.

The following equation computes the typical full-scale current

with respect to the Rset resistor value and the gain control

setting:



SET

OUT







0206

)

(

The DAC is designed to operate with full-scale current values

up to 4.58 mA. Based on the equation and assuming a 4.62 kΩ

resistor value for RSET, and x = 0x1FF, the nominal output

current for the DAC is 2.28 mA.

Figure 17 shows the range of DAC output current vs. the DAC

FS value assuming an RSET value of 4.62 kΩ.

1200

DAC CODE

200

400

600

800

1000

Figure 21. DAC Output Current vs. DAC FS Bits

Pay careful attention to the load termination to ensure that the

output voltage remains within the specified compliance range;

voltages developed beyond this range cause excessive distortion

and can damage the DAC output circuitry.

I/O PORT

The AD9913 I/O port can be configured as a synchronous serial

communications port that allows easy interface to many industry-

standard microcontrollers and microprocessors. The serial I/O port

is compatible with most synchronous transfer formats, including

both the Motorola 6905/11 SPI and Intel 8051 SSR protocols. For

faster programming requirements, a parallel mode is also provided.

PROFILE SELECTIONS

The AD9913 supports the use of profiles, which consist of a group

of eight registers containing pertinent operating parameters for

a particular operating mode. Profiles enable rapid switching

between parameter sets. Profile parameters are programmed via

the I/O port. Once programmed, a specific profile is activated

by means of Register CFR1 Bits [22:20], or three external profile

select pins. The external profile pins option is only available in

serial mode.

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