AD9834 Analog Devices, AD9834 Datasheet - Page 14

• Manufacturer Part Number: AD9834
• Description: +2.5V to +5.5V, 50MHz, Low Power (25mW) Complete DDS With on Board Comparator in 20-pin Tssop Package
• Manufacturer: Analog Devices

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.
OPBITEN MODE SIGNPIB DIV2
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.
OPBITEN Bit
AD9834
Bit
0
1
1
1
1
1
0
0
1
1
Table 13: Various Outputs from SIGN BIT OUT
Table 14: Various Outputs from IOUT/IOUTB
Bit
X
0
0
0
0
1
MODE Bit
0
1
0
1
Bit
X
0
0
1
1
X
PRELIMINARY TECHNICAL DATA
Bit
X
X
0
1
0
1
SIGN BIT OUT
High Impedance
DAC data MSB / 2
DAC data MSB
Reserved
Comparator Output
Reserved
IOUT / IOUTB Pins
Sinusoid
Up/Down Ramp
Sinusoid
Reserved
Pin
–14–
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.
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.
More complex modula-
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