AD9779PCB datasheet(25/34 Pages) AD

25 / 34 page

Preliminary Technical Data

AD9779

Rev. PrD | Page 25 of 34

Interpolation Filter Architecture

The AD9779 can provide up to 8× interpolation or disable the

interpolation filters entirely. The coefficients of the low pass filters

and the inverse sinc filter are given in Table 5, Table 6, Table 7, and

Table 8. Spectral plots for the filter responses are given in Figure 3,

Figure 4, and Figure 5.

With the interpolation filter and modulator combined, the

incoming signal can be placed anywhere within the Nyquist region

of the DAC output sample rate. Where the input signal is complex,

this architecture allows modulation of the input signal to positive

or negative Nyquist regions (refer to Table 13).

The Nyquist regions up to 4× the input data rate can be seen in

Figure 39.

1×

4×

3×

2×

-2×

-3×

-4×

-1×

1234

-1

-2

7 8

-3

-4

-5

-6

-7

-8

Figure 39. Nyquist Zones

Figure 3, Figure 4 and Figure 5 show the low pass response of the

digital filters with no modulation used. By turning on the

modulation feature, the response of the digital filters can be tuned

to any Nyquist zone within the DAC bandwidth. As an example,

Figure 40 to Figure 46 show the odd mode filter responses (refer to

Table 13 for odd/even mode filter responses).

-4

-3

-2

-1

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

Figure 40. Interpolation/Modulation Combination of -4fDAC/8

Filter in Odd Mode

-4

-3

-2

-1

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

Figure 41. Interpolation/Modulation Combination of -3fDAC/8

Filter in Odd Mode

-4

-3

-2

-1

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

Figure 42. Interpolation/Modulation Combination of -2fDAC/8

Filter in Odd Mode

-4

-3

-2

-1

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

Figure 43. Interpolation/Modulation Combination of -1fDAC/8

Filter in Odd Mode

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