Datasheet

AD9776A/AD9778A/AD9779A
Rev. B | Page 34 of 56
10
–100
–4
4
f
OUT
(× Input Data Rate)
ATTENUATION (dB)
–3–2–10123
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
06452-055
Figure 58. 4× Interpolation, Low-Pass Response to ±4× Input Data Rate
(Dotted Lines Indicate 1 dB Roll-Off)
10
–100
–4
4
f
OUT
(× Input Data Rate)
ATTENUATION (dB)
–3–2–10123
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
06452-056
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
in Figure 60.
–4
–
8
–3×
–
6
–2×
–
4
–1×
–
2
DC
1
1×
3
2×
5
3×
7
–
7
–
5
–
3
–
1246
4×
08
06452-086
Figure 60. Nyquist Zones
Figure 57, Figure 58, and Figure 59 show the low-pass response
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 61
to 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
–3–2–10123
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
f
OUT
(× Input Data Rate)
ATTENUATION (dB)
06452-058
Figure 61. Interpolation/Modulation Combination of 4f
DAC
/8 Filter
10
–100
–4
4
–3–2–10123
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
f
OUT
(× Input Data Rate)
ATTENUATION (dB)
06452-059
Figure 62. Interpolation/Modulation Combination of −3f
DAC
/8 Filter
10
–100
–4
4
–3–2–10123
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
f
OUT
(× Input Data Rate)
ATTENUATION (dB)
06452-060
Figure 63. Interpolation/Modulation Combination of −2f
DAC
/8 Filter