Analog Devices AD9776 Instruction Manual page 30

AD9776/AD9778/AD9779
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–4 –3
Figure 56. 8× Interpolation, Low-Pass Response to 19× Input Data Rate
(Dotted Lines Indicate 1 dB Roll-Off)
10
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
The Nyquist regions of up to 9× the input data rate can be seen
in
–8
–4×
100
–4
– 3 – 2 – 1 0 1 2 3
I n p u t D a t a R a t e ) ( × f
of the digital filters with no modulation used. By turning on the
modulation feature, the response of the digital filters can be
tuned to anywhere within the DAC bandwidth. As an example,
A
0
0
, Figure 55, and
0
Table 16 show the nonshifted mode filter res- Figure 64 Figure 54 Figure 58 to
D A C / 8 F i l t e r F i g u r e 5 8 . I n t e r p o l a t i o n / M o d u l a t i o n C o m b i n a t i o n o f 4 f – 3 – 2 – 1 0 1 2 3
–2 –1 0 1 2 3
f
(× Input Data Rate)
OUT
4
Figure 57. Nyquist Zones
show the low-pass response
).
4
Figure 59. Interpolation/Modulation Combination of –3f
Figure 60. Interpolation/Modulation Combination of –2f
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–4
Figure 61. Interpolation/Modulation Combination of –1f
Rev. 0 | Page 30 of 56
f o r s h i f t e d / n o n s h i f t e d m o d e f i l t e r T a b l e 1 6
–3 –2 –1 0 1 2
f
(× Input Data Rate)
OUT
O U T – 3 – 2 – 1 0 1 2 3
/8 Filter
DAC
/8 Filter
DAC
A
3 4
/8 Filter
DAC