AD9775EB AD [Analog Devices], AD9775EB Datasheet - Page 26

• Manufacturer Part Number: AD9775EB
• Description: 14-Bit, 160 MSPS 2X/4X/8X Interpolating Dual TxDAC+ D/A Converter
• Manufacturer: AD [Analog Devices]

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
Figure 25a. No Interpolation, Modulation Disabled
Figure 25b. No Interpolation, Modulation = f
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
0
0
0
0
0.2
0.2
Figure 25. Effects of Digital Modulation on DAC Output Spectrum, Interpolation Disabled
0.4
0.4
f
f
OUT
OUT
(
(
f
f
DATA
DATA
0.6
0.6
)
)
0.8
0.8
DAC
1.0
1.0
/2
–26–
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 f
are scaled by a factor of 2. In the situation where the modula-
tion is f
and there is no scaling effect.
Figure 25c. No Interpolation, Modulation = f
Figure 25d. No Interpolation, Modulation = f
–100
–100
S
–20
–40
–60
–80
–20
–40
–60
–80
/2, the modulated spectral components add constructively
0
0
0
0
0.2
0.2
0.4
0.4
f
f
OUT
OUT
(
(
f
f
DATA
DATA
0.6
0.6
)
)
0.8
0.8
S
DAC
DAC
/4 or f
1.0
1.0
REV. 0
/4
/8
S
/8)