Datasheet

AD9776/AD9778/AD9779
Rev. A | Page 32 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
05361-056
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 17).
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 –1 2 4 6 8
4×
05361-057
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
modulation 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
(refer to
Table 1 7 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)
05361-058
Figure 61. Interpolation/Modulation Combination of 4 f
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)
05361-059
Figure 62. Interpolation/Modulation Combination of −3 f
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)
05361-060
Figure 63. Interpolation/Modulation Combination of −2 f
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)
05361-061
Figure 64. Interpolation/Modulation Combination of −1 f
DAC
/8 Filter