AD9680 Datasheet, PDF (59/97 Pages) Analog Devices – Dual, 14-Bit, 1.25 GSPS, 1.2 V/2.5 V, Analog-to-Digital Converter

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AD9680
HB2 Filter
The third decimate-by-2, half-band, low-pass FIR filter (HB2)
uses a 19-tap, symmetrical, fixed coefficient filter implementation
that is optimized for low power consumption. The HB2 filter is
only used when complex outputs (decimate by 4, 8, or 16) or
real outputs (decimate by 2, 4, or 8) are enabled; otherwise, the
filter is bypassed.
Table 21 and Figure 152 show the coefficients and response of
the HB2 filter.
Table 21. HB2 Filter Coefficients
HB2 Coefficient
Number
Normalized
Coefficient
C1, C19
0.000614
C2, C18
0
C3, C17
−0.005066
C4, C16
0
C5, C15
0.022179
C6, C14
0
C7, C13
−0.073517
C8, C12
0
C9, C11
0.305786
C10
0.500000
Decimal Coefficient
(19-Bit)
161
0
−1328
0
5814
0
−19,272
0
80,160
131,072
0
–20
–40
–60
–80
–100
–120
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
NORMALIZED FREQUENCY (× π RAD/SAMPLE)
Figure 152. HB2 Filter Response
HB1 Filter
The fourth and final decimate-by-2, half-band, low-pass FIR
filter (HB1) uses a 55-tap, symmetrical, fixed coefficient filter
implementation, optimized for low power consumption. The
HB1 filter is always enabled and cannot be bypassed. Table 22
and Figure 153 show the coefficients and response of the HB1
filter.
0
–20
–40
–60
–80
–100
–120
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
NORMALIZED FREQUENCY (× π RAD/SAMPLE)
Figure 153. HB1 Filter Response
Table 22. HB1 Filter Coefficients
HB1 Coefficient
Number
Normalized
Coefficient
C1, C55
−0.000023
C2, C54
0
C3, C53
0.000097
C4, C52
0
C5, C51
−0.000288
C6, C50
0
C7, C49
0.000696
C8, C48
0
C9, C47
−0.0014725
C10, C46
0
C11, C45
0.002827
C12, C44
0
C13, C43
−0.005039
C14, C42
0
C15, C41
0.008491
C16, C40
0
C17, C39
−0.013717
C18, C38
0
C19, C37
0.021591
C20, C36
0
C21, C35
−0.033833
C22, C34
0
C23, C33
0.054806
C24, C32
0
C25, C31
−0.100557
C26, C30
0
C27, C29
0.316421
C28
0.500000
Decimal Coefficient
(21-Bit)
−24
0
102
0
−302
0
730
0
−1544
0
2964
0
−5284
0
8903
0
−14,383
0
22,640
0
−35,476
0
57,468
0
−105,442
0
331,792
524,288
Rev. C | Page 59 of 97