Datasheet

AD9777
Rev. C | Page 36 of 60
MODULATION, INTERMODULATION = 4×
With Control Register 01h, Bit 7 and Bit 6 set to 10, the
interpolation rate of the AD9777 is 4×. Modulation is achieved
by multiplying successive samples at the interpolation filter
output by the sequence (0, +1, 0, −1).
Figure 67 to Figure 70 represent the spectral response of the
AD9777 DAC output with 4× interpolation in the various
modulation modes to a narrow band baseband signal.
The Effects of Digital Modulation on DAC Output Spectrum, Interpolation = 4x
–100
–80
–60
–40
–20
0
AMPLITUDE (dBFS)
f
OUT
( × f
DATA
)
1023
02706-067
4
Figure 67. 4x Interpolation, Modulation Disabled
–100
–80
–60
–40
–20
0
AMPLITUDE (dBFS)
f
OUT
( × f
DATA
)
1023
02706-068
4
Figure 68. 4x Interpolation, Modulation = f
DAC
/2
–100
–80
–60
–40
–20
0
AMPLITUDE (dBFS)
f
OUT
( × f
DATA
)
1023
02706-069
4
Figure 69. 4x Interpolation, Modulation = f
DAC
/4
–100
–80
–60
–40
–20
0
AMPLITUDE (dBFS)
f
OUT
( × f
DATA
)
1023
02706-070
4
Figure 70. 4x Interpolation, Modulation = f
DAC
/8