Interpolation Filter Architecture - Analog Devices AD9776 Instruction Manual

INTERPOLATION FILTER ARCHITECTURE

The AD9776/AD9778/AD9779 can provide up to 8× interpola-
tion or disable the interpolation filters entirely. It is important
to note that the input signal should be backed off by approxima-
tely 0.01 dB from full scale to avoid overflowing the interpola-
tion filters. The coefficients of the low-pass filters and the
inverse sinc filter are given in Table 12, Table 13, Table 14,and
Table 15. Spectral plots for the filter responses are shown in
Figure 54, Figure 55, and Figure 56.
Table 12. Halfband Filter 1
Lower Coefficient
H(1)
H(2)
H(3)
H(4)
H(5)
H(6)
H(7)
H(8)
H(9)
H(10)
H(11)
H(12)
H(13)
H(14)
H(15)
H(16)
H(17)
H(18)
H(19)
H(20)
H(21)
H(22)
H(23)
H(24)
H(25)
H(26)
H(27)
H(28)
Table 13. Halfband Filter 2
Lower Coefficient
H(1)
H(2)
H(3)
H(4)
H(5)
H(6)
H(7)
H(8)
H(9)
I n p u t D a t a R a t e ) ( ×
H(10)
H(11)
H(12)
Upper Coefficient Integer Value
H(55) –4
H(54) 0
H(53) 13
H(52) 0
H(51) –34
H(50) 0
H(49) 72
H(48) 0
H(47) –138
H(46) 0
H(45) 245
H(44) 0
H(43) –408
H(42) 0
H(41) 650
H(40) 0
H(39) –1003
H(38) 0
H(37) 1521
H(36) 0
H(35) –2315
H(34) 0
H(33) 3671
H(32) 0
H(31) –6642
H(30) 0
H(29) 20755
32768
Upper Coefficient Integer Value
H(23) –2
H(22) 0
H(21) 17
H(20) 0
H(19) –75
H(18) 0
H(17) 238
H(16) 0
H(15) –660
H(14) 0
H(13) 2530
4096
Table 14. Halfband Filter 3
Lower Coefficient
H(1)
H(2)
H(3)
H(4)
H(5)
H(6)
H(7)
H(8)
Table 15. Inverse Sinc Filter
Lower Coefficient
H(1)
H(2)
H(3)
H(4)
H(5)
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–4 –3
Figure 54. 2× Interpolation, Low-Pass Response to ±4× Input Data Rate
(Dotted Lines Indicate 1 dB Roll-Off)
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
Figure 55. 4× Interpolation, Low-Pass Response to ±4× Input Data Rate
(Dotted Lines Indicate 1 dB Roll-Off)
Rev. 0 | Page 29 of 56
AD9776/AD9778/AD9779
Upper Coefficient Integer Value
H(15) –39
H(14) 0
H(13) 273
H(12) 0
H(11) –1102
H(10) 0
H(9) 4964
8192
Upper Coefficient Integer Value
H(9) 2
H(8) –4
H(7) 10
H(6) –35
401
–2 –1 0 1 2 3
f
(× Input Data Rate)
OUT
OUT
4