Datasheet
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 1 3, 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) 0
H(3) H(53) +13
H(4) H(52) 0
H(5) H(51) −34
H(6) H(50) 0
H(7) H(49) +72
H(8) H(48) 0
H(9) H(47) −138
H(10) H(46) 0
H(11) H(45) +245
H(12) H(44) 0
H(13) H(43) −408
H(14) H(42) 0
H(15) H(41) +650
H(16) H(40) 0
H(17) H(39) −1003
H(18) H(38) 0
H(19) H(37) +1521
H(20) H(36) 0
H(21) H(35) −2315
H(22) H(34) 0
H(23) H(33) +3671
H(24) H(32) 0
H(25) H(31) −6642
H(26) H(30) 0
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) 0
H(3) H(21) +17
H(4) H(20) 0
H(5) H(19) −75
H(6) H(18) 0
H(7) H(17) +238
H(8) H(16) 0
H(9) H(15) −660
H(10) H(14) 0
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) 0
H(3) H(13) +273
H(4) H(12) 0
H(5) H(11) −1102
H(6) H(10) 0
H(7) H(9) +4964
H(8) +8192
Table 16. Inverse Sinc Filter
Lower Coefficient Upper Coefficient Integer Value
H(1) H(9) +2
H(2) H(8) −4
H(3) H(7) +10
H(4) H(6) −35
H(5) +401
10
–100
–4
4
f
OUT
(× Input Data Rate)
ATTENUATION (dB)
–3–2–10123
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
05361-054
Figure 57. 2× Interpolation, Low-Pass Response to ±4× Input Data Rate
(Dotted Lines Indicate 1 dB Roll-Off)
10
–100
–4
4
f
OUT
(× Input Data Rate)
ATTENUATION (dB)
–3–2–10123
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
05361-055
Figure 58. 4× Interpolation, Low-Pass Response to ±4× Input Data Rate
(Dotted Lines Indicate 1 dB Roll-Off)