AD9776-EB datasheet(31/56 Pages) AD

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AD9776/AD9778/AD9779

Rev. A | Page 31 of 56

INTERPOLATION FILTER ARCHITECTURE

The AD9776/AD9778/AD9779 can provide up to 8× interpola-

tion, or the interpolation filters can be entirely disabled. It is

important to note that the input signal should be backed off by

approximately 0.01 dB from full scale to avoid overflowing the

interpolation filters. The coefficients of the low-pass filters and

the inverse sinc filter are given in Table 13, Table 14, Table 15,

and Table 16. Spectral plots for the filter responses are shown in

Figure 57, Figure 58, and Figure 59.

Table 13. Half-Band Filter 1

Lower Coefficient

Upper Coefficient

Integer Value

H(1)

H(55)

−4

H(2)

H(54)

H(3)

H(53)

+13

H(4)

H(52)

H(5)

H(51)

−34

H(6)

H(50)

H(7)

H(49)

+72

H(8)

H(48)

H(9)

H(47)

−138

H(10)

H(46)

H(11)

H(45)

+245

H(12)

H(44)

H(13)

H(43)

−408

H(14)

H(42)

H(15)

H(41)

+650

H(16)

H(40)

H(17)

H(39)

−1003

H(18)

H(38)

H(19)

H(37)

+1521

H(20)

H(36)

H(21)

H(35)

−2315

H(22)

H(34)

H(23)

H(33)

+3671

H(24)

H(32)

H(25)

H(31)

−6642

H(26)

H(30)

H(27)

H(29)

+20,755

H(28)

+32,768

Table 14. Half-Band Filter 2

Lower Coefficient

Upper Coefficient

Integer Value

H(1)

H(23)

−2

H(2)

H(22)

H(3)

H(21)

+17

H(4)

H(20)

H(5)

H(19)

−75

H(6)

H(18)

H(7)

H(17)

+238

H(8)

H(16)

H(9)

H(15)

−660

H(10)

H(14)

H(11)

H(13)

+2530

H(12)

+4096

Table 15. Half-Band Filter 3

Lower Coefficient

Upper Coefficient

Integer Value

H(1)

H(15)

−39

H(2)

H(14)

H(3)

H(13)

+273

H(4)

H(12)

H(5)

H(11)

−1102

H(6)

H(10)

H(7)

H(9)

+4964

H(8)

+8192

Table 16. Inverse Sinc Filter

Lower Coefficient

Upper Coefficient

Integer Value

H(1)

H(9)

H(2)

H(8)

−4

H(3)

H(7)

+10

H(4)

H(6)

−35

H(5)

+401

–100

–4

fOUT (× Input Data Rate)

–3

–2

–1

0123

–10

–20

–30

–40

–50

–60

–70

–80

–90

Figure 57. 2× Interpolation, Low-Pass Response to ±4× Input Data Rate

(Dotted Lines Indicate 1 dB Roll-Off)

–100

–4

fOUT (× Input Data Rate)

–3

–2

–1

0123

–10

–20

–30

–40

–50

–60

–70

–80

–90

Figure 58. 4× Interpolation, Low-Pass Response to ±4× Input Data Rate

(Dotted Lines Indicate 1 dB Roll-Off)

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