EVAL-AD7763EBZ Analog Devices Inc, EVAL-AD7763EBZ Datasheet - Page 24

• Manufacturer Part Number: EVAL-AD7763EBZ
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD7763EBZ

• Lead Free Status / Rohs Status: Supplier Unconfirmed

AD7763
PROGRAMMABLE FIR FILTER
As discussed in the Theory of Operation section, the third FIR
filter on the AD7763 can be programmed by the user. The default
coefficients that are loaded on reset are shown in Table 12. This
gives the frequency response shown in Figure 37. The frequencies
shown in Figure 37 scale directly with the output data rate.
Table 12. Default Filter Coefficients
#
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
The default filter should be sufficient for most applications.
It is a standard brick wall filter with a symmetrical impulse
response. The default filter has a length of 96 taps and is
nonaliasing, with 120 dB of attenuation at Nyquist. This filter
not only performs signal antialiasing but also suppresses out-of-
band quantization noise produced by the analog-to-digital
conversion process. Any significant relaxation in the stop-band
attenuation or transition bandwidth relative to the default filter
can result in failure to meet the SNR specifications.
Decimal
Value
[phone]
[phone]
−4497814
−11935847
−1313841
+6976334
+3268059
−3794610
−3747402
+1509849
+3428088
+80255
−2672124
−1056628
+1741563
+1502200
−835960
−1528400
+93626
+1269502
+411245
−864038
−664622
+434489
Hex
Value
332BCA0
17FA5A0
444A196
4B62067
4140C31
6A734E
31DDDB
439E6B2
4392E4A
1709D9
344EF8
1397F
428C5FC
4101F74
1A92FB
16EBF8
40CC178
4175250
16DBA
135EFE
6466D
40D2F26
40A242E
6A139
#
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
Decimal
Value
+700847
−70922
−583959
−175934
+388667
+294000
−183250
−302597
+16034
+238315
+88266
−143205
−128919
+51794
+121875
+16426
−90524
−63899
+45234
+114720
+102357
+52669
+15559
+1963
B0B2
Hex
Value
AB1AF
401150A
408E917
402AF3E
5EE3B
47C70
402CBD2
4049E05
3EA2
3A2EB
158CA
4022F65
401F797
CA52
1DC13
402A
401619C
400F99B
1C020
18FD5
CDBD
3CC7
7AB
Rev. 0 | Page 24 of 32
To create a user-defined filter, note the following:
• The filter must be even, symmetrical FIR.
• The coefficients are 27 bits in length. All coefficients are
• The filter length must be between 12 taps and 96 taps in
• Because the filter is symmetrical, the number of coefficients
• Coefficients are written from the center of impulse response
• The coefficients are scaled so that the in-band gain
To download a user-defined filter, see the Downloading a User-
Defined Filter section.
in sign-and-magnitude format. The sign bit coded as
positive = 0 is followed by 26 magnitude bits.
steps of 12.
that must be downloaded is half the filter length. The default
filter coefficients are an example of this, with only 48
coefficients listed for a 96-tap filter.
(adjacent to the point of symmetry) outward.
of the filter is equal to 134217726, with the coefficients
rounded to the nearest integer. For a low-pass filter, this is the
equivalent of having the coefficients sum arithmetically
(including sign) to [phone] (0x3FFFFFF) positive value
over the half-impulse-response coefficient set (maximum 48
coefficients). Any deviation from this results in the
introduction of a gain error.
–100
–120
–140
–160
–20
–40
–60
–80
Figure 37. Default Filter Frequency Response (625 kHz ODR)
0
0
100
200
FREQUENCY (kHz)
300
–0.1dB FREQUENCY = 251kHz
PASS-BAND RIPPLE = 0.05dB
–3dB FREQUENCY = 256kHz
STOP BAND = 312.5kHz
400
500
600