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AD9834

–14–

REV PrM

PRELIMINARY TECHNICAL DATA

Comparator Output:

The AD9834 has an on-board

comparator. To connect this comparator to the SIGN

BIT OUT pin, the SIGNPIB (D4) control bit must be set

to 1. After filtering the sinusoidal output from the DAC,

the waveform can be applied to the comparator to generate

a square waveform.

MSB from the NCO: The MSB from the NCO can be

output from the AD9834. By setting the SIGNPIB (D4)

control bit to 0, the MSB of the DAC data is available at

the SIGN BIT OUT pin. This is useful as a coarse clock

source. This square wave can also be divided by 2 before

being output. The bit DIV2 (D3) in the control register

controls the frequency of this output from the SIGN BIT

OUT pin.

Table 13: Various Outputs from SIGN BIT OUT

OPBITEN MODE

SIGNPIB DIV2

SIGNBITOUT

Bit

High Impedance

DAC data MSB / 2

DAC data MSB

Reserved

Comparator Output

Reserved

The IOUT/IOUTB Pins

The analog outputs from the AD9834 are available from

the IOUT/IOUTB pins. The available outputs are a

sinuoidal output or a ramp output.

Sinusoidal Output: The SIN ROM is used to convert the

phase information from the frequency and phase registers

into amplitude information which results in a sinusoidal

signal at the output. To have a sinusoidal output from the

IOUT/IOUTB pins set the bt MODE (D1) = 1.

Up/Down Ramp Output: The SIN ROM can be bypassed

so that the truncated digital output from the NCO is sent

to the DAC.

In this case, the output is no longer sinusoi-

dal.

The DAC will produce a ramp up/down function. To

have a ramp output from the IOUT/IOUTB pins set the

bt MODE (D1) = 0.

Note that the SLEEP pin/SLEEP12 bit must be 0 (i.e. the

DAC is enabled) when using these pins.

Table 14: Various Outputs from IOUT/IOUTB

OPBITENBit

MODEBit

IOUT / IOUTB Pins

Sinusoid

Up/Down Ramp

Sinusoid

Reserved

APPLICATIONS

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 modu-

lation applications.

The part can be used to perform

simple modulation such as FSK.

More complex modula-

tion 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

will represent the space frequency while the other will

represent the mark frequency. The digital data stream is

fed to the FSELECT pin which will cause the AD9834 to

modulate the carrier frequency between the two values.

The AD9834 has two phase registers; this enables the part

to perform PSK. With phase shift keying, the carrier fre-

quency is phase shifted, the phase being altered by an

amount which is related to the bit stream being input to

the modulator.

The AD9834 is also suitable for signal generator applica-

tions. 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 in which it can be used as a local oscillator.

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