Interpolation Filter Architecture - Analog Devices AD9776A Manual

INTERPOLATION FILTER ARCHITECTURE

The AD9776A/AD9778A/AD9779A can provide up to 8× inter-
polation, 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 15, Table 16, Table 17,
and Table 18. Spectral plots for the filter responses are shown in
Figure 57, Figure 58, and Figure 59.
Table 15. Low-Pass Filter 1
Lower Coefficient Upper Coefficient
H(1) H(55)
H(2) H(54)
H(3) H(53)
H(4) H(52)
H(5) H(51)
H(6) H(50)
H(7) H(49)
H(8) H(48)
H(9) H(47)
H(10) H(46)
H(11) H(45)
H(12) H(44)
H(13) H(43)
H(14) H(42)
H(15) H(41)
H(16) H(40)
H(17) H(39)
H(18) H(38)
H(19) H(37)
H(20) H(36)
H(21) H(35)
H(22) H(34)
H(23) H(33)
H(24) H(32)
H(25) H(31)
H(26) H(30)
H(27) H(29)
H(28)
Table 16. Low-Pass Filter 2
Lower Coefficient
H(1)
H(2)
H(3)
H(4)
H(5)
H(6)
H(7)
H(8)
Integer Value
H(9)
−4
H(10)
0
H(11)
+13
H(12)
0
−34
Table 17. Low-Pass Filter 3
0
Lower Coefficient
+72
H(1)
0
H(2)
−138
H(3)
0
H(4)
+245
H(5)
0
H(6)
−408
H(7)
0
H(8)
+650
0
Table 18. Inverse Sinc Filter
−1003
Lower Coefficient
0
H(1)
+1521
H(2)
0
H(3)
−2315
H(4)
0
H(5)
+3671
0
−6642
0
+20,755
+32,768
Rev. B | Page 33 of 56
AD9776A/AD9778A/AD9779A
Upper Coefficient
H(23)
H(22)
H(21)
H(20)
H(19)
H(18)
H(17)
H(16)
H(15)
H(14)
H(13)
Upper Coefficient
H(15)
H(14)
H(13)
H(12)
H(11)
H(10)
H(9)
Upper Coefficient
H(9)
H(8)
H(7)
H(6)
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–4 –3 –2 –1
f
(× Input Data Rate)
OUT
Figure 57. 2× Interpolation, Low-Pass Response to ±4× Input Data Rate
(Dotted Lines Indicate 1 dB Roll-Off)
Integer Value
−2
0
+17
0
−75
0
+238
0
−660
0
+2530
+4096
Integer Value
−39
0
+273
0
−1102
0
+4964
+8192
Integer Value
+2
−4
+10
−35
+401
0 1 2 3 4