Datasheet

AD9775
Rev. E | Page 34 of 56
MODULATION, INTERPOLATION = 4×
With Control Register 0x01, Bit 7 and Bit 6 set to 10, the
interpolation rate of the AD9775 is 4×. Modulation is achieved
by multiplying successive samples at the interpolation filter
output by the sequence (0, +1, 0, −1).
Figure 67 through Figure 70 represent the spectral response of
the AD9775 DAC output with 4× interpolation in the various
modulation modes to a narrow-band baseband signal.
The Effects of the Digital Modulation on the DAC Output Spectrum, Interpolation = 4×
–100
–80
–60
–40
–20
0
AMPLITUDE (dBFS)
f
OUT
(× f
DATA
)
1023
02858-067
4
Figure 67. 4× Interpolation, Modulation Disabled
–100
–80
–60
–40
–20
0
AMPLITUDE (dBFS)
f
OUT
(× f
DATA
)
1023
02858-068
4
Figure 68. 4× Interpolation, Modulation = f
DAC
/4
–100
–80
–60
–40
–20
0
AMPLITUDE (dBFS)
f
OUT
(× f
DATA
)
1023
02858-069
4
Figure 69. 4× Interpolation, Modulation = f
DAC
/2
–100
–80
–60
–40
–20
0
AMPLITUDE (dBFS)
f
OUT
(× f
DATA
)
1023
02858-070
4
Figure 70. 4× Interpolation, Modulation = f
DAC
/8