AD9776A/AD9778A/AD9779A
Rev. B | Page 34 of 56
10
–100
–4
4
fOUT (× Input Data Rate)
AT
T
E
N
UAT
IO
N
(
d
B
)
–3
–2
–1
0123
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
06
45
2-
0
55
Figure 58. 4× Interpolation, Low-Pass Response to ±4× Input Data Rate
(Dotted Lines Indicate 1 dB Roll-Off)
10
–100
–4
4
fOUT (× Input Data Rate)
AT
T
E
N
UAT
IO
N
(
d
B
)
–3
–2
–1
0123
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
06
45
2-
0
56
Figure 59. 8× Interpolation, Low-Pass Response to ±4× Input Data Rate
(Dotted Lines Indicate 1 dB Roll-Off)
With the interpolation filter and modulator combined, the
incoming signal can be placed anywhere within the Nyquist
region of the DAC output sample rate. When the input signal
is complex, this architecture allows modulation of the input
signal to positive or negative Nyquist regions (see
Table 19).
The Nyquist regions of up to 4× the input data rate can be seen
–4
–8
–3×
–6
–2×
–4
–1×
–2
DC
1
1×
3
2×
5
3×
7
–7
–5
–3
–12
4
6
4×
08
06
45
2-
08
6
Figure 60. Nyquist Zones
of the digital filters with no modulation. By turning on the modu-
lation feature, the response of the digital filters can be tuned to
anywhere within the DAC bandwidth. As an example,
Figure 61to
Figure 67 show the nonshifted mode filter responses for 8×
interpolation (refer to
Table 19 for shifted/nonshifted mode
filter responses).
10
–100
–4
4
–3
–2
–1
0123
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
fOUT (× Input Data Rate)
AT
T
E
N
UAT
IO
N
(
d
B
)
06
45
2-
0
58
Figure 61. Interpolation/Modulation Combination of 4fDAC/8 Filter
10
–100
–4
4
–3
–2
–1
0123
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
fOUT (× Input Data Rate)
AT
T
E
N
UAT
IO
N
(
d
B
)
06
45
2-
0
59
Figure 62. Interpolation/Modulation Combination of 3fDAC/8 Filter
10
–100
–4
4
–3
–2
–1
0123
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
fOUT (× Input Data Rate)
AT
T
E
N
UAT
IO
N
(
d
B
)
06
45
2-
0
60
Figure 63. Interpolation/Modulation Combination of 2fDAC/8 Filter