AD9834 datasheet(22/32 Pages) AD

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AD9834

Data Sheet

Table 16. Applying the SLEEP Function

SLEEP

SLEEP1

Bit

SLEEP12

Bit

PIN/SW

Bit

Result

No power-down

DAC powered

down

No power-down

DAC powered

down

Internal clock

disabled

Both the DAC

powered down

and the internal

clock disabled

DAC Powered Down

This is useful when the AD9834 is used to output the MSB of

the DAC data only. In this case, the DAC is not required and

can be powered down to reduce power consumption.

Internal Clock Disabled

When the internal clock of the AD9834 is disabled, the DAC

output remains at its present value because the NCO is no

longer accumulating. New frequency, phase, and control words

can be written to the part when the SLEEP1 control bit is active.

The synchronizing clock remains active, meaning that the

selected frequency and phase registers can also be changed

either at the pins or by using the control bits. Setting the

SLEEP1 bit to 0 enables the MCLK. Any changes made to the

registers when SLEEP1 is active are observed at the output after

a certain latency.

The effect of asserting the SLEEP pin is evident immediately at

the output, that is, the zero-to-one transition of this pin is not

sampled. However, the negative transition of SLEEP is sampled

on the internal falling edge of MCLK.

SIGN BIT OUT PIN

The AD9834 offers a variety of outputs from the chip. The

digital outputs are available from the SIGN BIT OUT pin. The

available outputs are the comparator output or the MSB of the

DAC data. The bits controlling the SIGN BIT OUT pin are

outlined in Table 17.

This pin must be enabled before use. The enabling/disabling of

this pin is controlled by the Bit OPBITEN (DB5) in the control

MODE bit (DB1) in the control register should be set to 0 if

OPBITEN = 1.

Comparator Output

The AD9834 has an on-board comparator. To connect this

comparator to the SIGN BIT OUT pin, the SIGN/PIB (DB4)

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 SIGN/PIB (DB4) 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 two before being output. Bit DIV2 (DB3) in the control register

controls the frequency of this output from the SIGN BIT OUT pin.

Table 17. Various Outputs from SIGN BIT OUT

OPBITEN

Bit

MODE

Bit

SIGN/PIB

Bit

DIV2

Bit

SIGN BIT OUT Pin

High impedance

DAC data MSB/2

DAC data MSB

Reserved

Comparator output

Reserved

THE IOUT AND IOUTB PINS

The analog outputs from the AD9834 are available from the

IOUT and IOUTB pins. The available outputs are a sinusoidal

output or a triangle output.

Sinusoidal Output

The SIN ROM converts the phase information from the

frequency and phase registers into amplitude information,

resulting in a sinusoidal signal at the output. To have a

sinusoidal output from the IOUT and IOUTB pins, set

Bit MODE (DB1) to 0.

Triangle 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 sinusoidal. The DAC produces 10-bit linear

triangular function. To have a triangle output from the IOUT

and IOUTB pins, set Bit MODE (DB1) to 1.

Note that the SLEEP pin and SLEEP12 bit must be 0 (that is, the

DAC is enabled) when using the IOUT and IOUTB pins.

Table 18. Various Outputs from IOUT and IOUTB

OPBITEN Bit

MODE Bit

IOUT and IOUTB Pins

Sinusoid

Triangle

Sinusoid

Reserved

3π/2

7π/2

11π/2

VOUT MAX

VOUT MIN

Figure 30. Triangle Output

Rev. D | Page 22 of 32

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