AD9775-EB Analog Devices, Inc., AD9775-EB Datasheet - Page 32

• Manufacturer Part Number: AD9775-EB
• Description: 14-bit, 160 Msps, 2?/4?/8? Interpolating Dual Txdac+ Digital-to-analog Converter
• Manufacturer: Analog Devices, Inc.

AD9775
MODULATION, NO INTERPOLATION
With Control Register 0x01, Bit 7 and Bit 6 set to 00, the
interpolation function on the AD9775 is disabled. Figure 59
through Figure 62 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 0x01, Bit 5 and Bit 4.
The tall rectangles represent the digital domain spectrum of a
baseband signal of narrow bandwidth. By comparing the digital
The Effects of the Digital Modulation on the DAC Output Spectrum, Interpolation Disabled
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
0
0
0
0
Figure 59. No Interpolation, Modulation Disabled
Figure 60. No Interpolation, Modulation = f
0.2
0.2
0.4
0.4
f
f
OUT
OUT
( ×
( ×
f
f
DATA
DATA
0.6
0.6
)
)
0.8
0.8
DAC
/2
1.0
1.0
Rev. E | Page 32 of 56
domain spectrum to the DAC sin(x)/x roll-off, an estimate can
be made for the characteristics required for the DAC recon-
struction filter.
Note also, per the previous discussion on amplitude
modulation, that the spectral components (where modulation is
set to f
where the modulation is f
components add constructively, and there is no
scaling effect.
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
0
0
S
/4 or f
0
0
Figure 61. No Interpolation, Modulation = f
Figure 62. No Interpolation, Modulation = f
S
/8) are scaled by a factor of 2. In the situation
0.2
0.2
S
0.4
0.4
/2, the modulated spectral
f
f
OUT
OUT
( ×
( ×
f
f
DATA
DATA
0.6
0.6
)
)
0.8
0.8
DAC
DAC
/4
/8
1.0
1.0