AD9834 datasheet(23/32 Pages) AD

23 / 32 page

Data Sheet

AD9834

Rev. D | Page 23 of 32

APPLICATIONS INFORMATION

Because of the various output options available from the part,

the AD9834 can be configured to suit a wide variety of

applications.

One of the areas where the AD9834 is suitable is in modulation

applications. The part can be used to perform simple modulation

such as FSK. More complex modulation schemes such as GMSK

and QPSK can also be implemented using the AD9834.

In an FSK application, the two frequency registers of the

AD9834 are loaded with different values. One frequency

represents the space frequency, and the other represents the

mark frequency. The digital data stream is fed to the FSELECT

pin, causing the AD9834 to modulate the carrier frequency

between the two values.

The AD9834 has two phase registers, enabling the part to

perform PSK. With phase shift keying, the carrier frequency is

phase shifted, the phase being altered by an amount that is

related to the bit stream that is input to the modulator.

The AD9834 is also suitable for signal generator applications.

With the on-board comparator, the device can be used to

generate a square wave.

With its low current consumption, the part is suitable for

applications where it is used as a local oscillator.

CHANGE PHASE?

CHANGE FREQUENCY?

YES

DAC OUTPUT

VOUT = VREFOUT × 18 × RLOAD/RSET × (1 + (SIN(2π(FREQREG × fMCLK × t/228 + PHASEREG/212))))

INITIALIZATION

SEE FIGURE 32

SELECT DATA

SOURCES

SEE FIGURE 34

WAIT 8/9 MCLK

CYCLES

SEE TIMING DIAGRAM

FIGURE 3

CHANGE PSEL/

PSELECT?

CHANGE PHASE

CHANGE DAC OUTPUT

FROM SIN TO RAMP?

CHANGE OUTPUT AT

SIGN BIT OUT PIN?

CHANGE FSEL/

FSELECT?

CHANGE FREQUENCY

CONTROL

WRITE

DATA WRITE

SEE FIGURE 33

Figure 31. Flow Chart for Initialization and Operation

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