AD9777BSVZ Datasheet, PDF (37/60 Pages) Analog Devices – 16-Bit, 160 MSPS 2x/4x/8x Interpolating Dual TxDAC+ D/A Converter

MODULATION, INTERMODULATION = 8×
With Control Register 01h, Bits 7 and 6, set to 11, the
interpolation rate of the AD9777 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 to Figure 74 represent the spectral response
of the AD9777 DAC output with 8× interpolation in the various
modulation modes to a narrow band baseband signal.
AD9777
Looking at Figure 59 to Figure 75, the user can see how higher
interpolation rates reduce the complexity of the reconstruction
filter needed at the DAC output. It also becomes apparent that
the ability to modulate by fS/2, fS/4, or fS/8 adds a degree of
flexibility in frequency planning
The Effects of the Digital Modulation on the DAC Output Spectrum, Interpolation = 8×
0
0
–20
–20
–40
–40
–60
–60
–80
–80
–100
0
1
2
3
4
f_OUT (×f_DATA)
Figure 71. 8× Interpolation, Modulation Disabled
0
–20
–40
–60
–80
–100
0
1
2
3
4
5
6
7
8
f_OUT (×f_DATA)
Figure 73. 8x Interpolation, Modulation = fDAC/4
0
–20
–40
–60
–80
–100
0
1
2
3
4
f_OUT (×f_DATA)
Figure 72. 8x Interpolation, Modulation = fDAC/2
–100
0
1
2
3
4
5
6
7
8
f_OUT (×f_DATA)
Figure 74. 8x Interpolation, Modulation = fDAC/8
Rev. C | Page 37 of 60