AD9775EB View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
AD9775EB Datasheet PDF : 48 Pages
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AD9775
MODULATION, NO INTERPOLATION
With Control Register 01h, Bits 7 and 6 set to “00,” the inter-
polation function on the AD9775 is disabled. Figures 25a–25d
show the DAC output spectral characteristics of the AD9775 in
the various modulation modes, all with the interpolation filters
disabled. The modulation frequency is determined by the state
of Control Register 01h, Bits 5 and 4. The tall rectangles
represent the digital domain spectrum of a baseband signal of
narrow bandwidth. By comparing the digital domain spectrum
to the DAC SIN(x)/x roll-off, an estimate can be made for the
characteristics required for the DAC reconstruction filter. Note
also, per the previous discussion on amplitude modulation, that
the spectral components (where modulation is set to fS/4 or fS/8)
are scaled by a factor of 2. In the situation where the modula-
tion is fS/2, the modulated spectral components add constructively
and there is no scaling effect.
0
0
–20
–20
–40
–40
–60
–60
–80
–80
–100
0
0.2
0.4
0.6
0.8
1.0
fOUT (؋fDATA)
Figure 25a. No Interpolation, Modulation Disabled
0
–100
0
0.2
0.4
0.6
fOUT (؋fDATA)
0.8
1.0
Figure 25c. No Interpolation, Modulation = fDAC/4
0
–20
–20
–40
–40
–60
–60
–80
–80
–100
0
0.2
0.4
0.6
0.8
1.0
fOUT (؋fDATA)
Figure 25b. No Interpolation, Modulation = fDAC/2
–100
0
0.2
0.4
0.6
fOUT (؋fDATA)
0.8
1.0
Figure 25d. No Interpolation, Modulation = fDAC/8
Figure 25. Effects of Digital Modulation on DAC Output Spectrum, Interpolation Disabled
–26–
REV. 0
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