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AD9713BBP View Datasheet(PDF) - Analog Devices

Part Name
Description
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AD9713BBP
ADI
Analog Devices ADI
AD9713BBP Datasheet PDF : 12 Pages
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AD9712B/AD9713B
SYSTEM
CLOCK
TUNING 32
WORD
NUMERICALLY-CONTROLLED OSCILLATOR
PHASE
14
ACCUMULATOR
PHASE-TO-AMPLITUDE
CONVERSION
OUTPUT 12
SINE DATA
TTL
12
REGISTER
LATCH
D1
ENABLE
AD9712B
AD9713B
D12 D/A CONVERTER
Figure 6. Direct Digital Synthesizer Block Diagram
When the analog frequency (fA) is exactly fC/N and N is an even
integer, the DDS continually uses a small subset of the available
DAC codes. The DNL of the converter is effectively the DNL
error of the codes used, and is typically worse than the error
measured against all available DAC codes. This increase in
DNL is translated into higher harmonic and noise levels at the
output.
Glitch impulse, often considered a figure of merit in DDS appli-
cations, is simply the initial transient response of the DAC as it
moves between two output levels. This nonlinearity is com-
monly associated with external data skew, but this effect is mini-
mized by using the on-board registers of the AD9712B/AD9713B
converters (see Digital Inputs/Timing section). The majority of
the glitch impulse, shown below, is produced as the current in
the R-2R ladder network settles, and is fairly constant over the
full-scale range of the DAC. The fast transients which form the
glitch impulse appear as high-frequency spurs in the output
spectrum.
While it is difficult to predict the effects of glitch on the output
waveform, slew rate limitations translate directly into harmonics.
This makes slew rate the dominant effect in ac linearity of the
DAC. Applications in which the ratio of analog frequency (fA)
to clock frequency (fC) is relatively high will benefit from the
high slew rate and low output capacitance of the AD9712B/
AD9713B devices.
Another concern in DDS applications is the presence of aliased
harmonics in the output spectrum. Aliased harmonics appear as
spurs in the output spectrum at frequencies which are deter-
mined by:
MfA ± NfC
where M and N are integers.
The effects of these spurs are most easily observed in applica-
tions where fA is nearly equal to an integer fraction of the clock
rate. This condition causes the aliased harmonics to fold near
the fundamental output frequency (see Performance Curves.)
100
90
5mV/div
10
0%
5ns/div
Figure 7. AD9712B/AD9713B Glitch Impulse
200mV/div
100
90
10
0%
1ns/div
Figure 8. Rise and Fall Characteristics
–8–
REV. B
 

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