AD9775-EB Analog Devices, Inc., AD9775-EB Datasheet - Page 35

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

MODULATION, INTERPOLATION = 8×
With Control Register 0x01, Bit 7 and Bit 6 set to 11, the
interpolation rate of the AD9775 is 8×. Modulation is achieved
by multiplying successive samples at the interpolation filter
output by the sequence (0, +0.707, +1, +0.707, 0, −0.707, −1,
+0.707). Figure 71 through Figure 74 represent the spectral
response of the AD9775 DAC output with 8× interpolation in the
various modulation modes to a narrow-band baseband signal.
The Effects of the Digital Modulation on the DAC Output Spectrum, Interpolation = 8×
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
0
0
0
0
Figure 71. 8× Interpolation, Modulation Disabled
Figure 72. 8× Interpolation, Modulation = f
1
1
f
f
OUT
OUT
(×
(×
2
2
f
f
DATA
DATA
)
)
3
3
DAC
/2
4
4
Rev. E | Page 35 of 56
Looking at Figure 63 through Figure 74, the user can see how
higher interpolation rates reduce the complexity of the recon-
struction filter needed at the DAC output. It also becomes
apparent that the ability to modulate by f
degree of flexibility in frequency planning.
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
0
0
0
0
Figure 73. 8× Interpolation, Modulation = f
Figure 74. 8× Interpolation, Modulation = f
1
1
2
2
3
3
f
f
OUT
OUT
(×
(×
4
4
f
f
DATA
DATA
)
)
5
5
S
/2, f
6
6
S
/4, or f
DAC
DAC
7
7
/4
/8
AD9775
S
/8 adds a
8
8