Analog Devices AD9776A Manual page 34

AD9776A/AD9778A/AD9779A
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–4 –3 –2 –1
f
OUT
Figure 58. 4× Interpolation, Low-Pass Response to ±4× Input Data Rate
(Dotted Lines Indicate 1 dB Roll-Off)
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–4 –3 –2 –1
f
OUT
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.
–8 –7 –6 –5 –4 –3 –2 –1
–4 –3× –2× –1×
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).
0 1 2 3
(× Input Data Rate)
0 1 2 3
(× Input Data Rate)
0 1 2 3 4 5 6 7 8
DC 1× 2× 3× 4×
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
4 –4
Figure 61. Interpolation/Modulation Combination of 4f
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–4
4
Figure 62. Interpolation/Modulation Combination of −3f
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–4
Figure 63. Interpolation/Modulation Combination of −2f
Rev. B | Page 34 of 56
–3 –2 –1 0 1
f
(× Input Data Rate)
OUT
–3 –2 –1 0 1
f
(× Input Data Rate)
OUT
–3 –2 –1 0 1
f
(× Input Data Rate)
OUT
2 3 4
/8 Filter
DAC
2 3 4
/8 Filter
DAC
2 3 4
/8 Filter
DAC