AD7760BSVZ Analog Devices Inc, AD7760BSVZ Datasheet - Page 30

• Manufacturer Part Number: AD7760BSVZ
• Description: IC ADC 24BIT 2.5MSPS 64TQFP
• Manufacturer: Analog Devices Inc

Specifications of AD7760BSVZ

• Data Interface: Parallel
• Number Of Bits: 24
• Sampling Rate (per Second): 2.5M
• Number Of Converters: 1
• Power Dissipation (max): 958mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 64-TQFP Exposed Pad
• Resolution (bits): 24bit
• Sampling Rate: 2.5MSPS
• Input Channel Type: Differential
• Supply Voltage Range - Digital: 2.375V To 2.625V
• Supply Current: 49mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7760
PROGRAMMABLE FIR FILTER
As previously mentioned, the third FIR filter on the AD7760
is user programmable. The default coefficients that are loaded
upon reset are given in Table 10, and the frequency responses
are shown in Figure 57. The frequencies quoted in Figure 57
scale directly with the output data rate.
Table 10. Default Filter Coefficients
No.
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, is nonaliasing, and provides
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 a failure to
meet the SNR specifications.
The default filter characteristics scale with both the MCLK
frequency applied and the decimation rate chosen by the user.
Dec
Value
53656736
25142688
−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
No.
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
Dec
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
Hex
Value
AB1AF
401150A
408E917
402AF3E
5EE3B
47C70
402CBD2
4049E05
3EA2
3A2EB
158CA
4022F65
401F797
CA52
1DC13
402A
401619C
400F99B
B0B2
1C020
18FD5
CDBD
3CC7
7AB
Rev. A | Page 30 of 36
To create a filter, note the following:
•
•
•
•
•
•
The procedure for downloading a user-defined filter is detailed
in the Downloading a User-Defined Filter section.
The filter must be an even, symmetrical FIR.
The coefficients are in sign-and-magnitude format, with
26 magnitude bits and sign coded as positive = 0.
The filter length must be between 12 taps and 96 taps in
steps of 12.
Because the filter is symmetrical, the number of
coefficients that must be downloaded is half the filter
length. The default filter coefficients exemplify this with
only 48 coefficients listed for a 96-tap filter.
Coefficients are written from the center of the impulse
response (adjacent to the point of symmetry) outwards.
The coefficients are scaled so that the in-band gain of the
filter is equal to 134,217,726, with the coefficients rounded
to the nearest integer. For a low-pass filter, this is the
equivalent of having the coefficients summed arithmetically
(including sign) to a +67,108,863 (0x3FF FFFF) positive
value over the half-impulse-response coefficient set (a
maximum of 48 coefficients). Any deviation from this
introduces a gain error.
–100
–120
–140
–160
–20
–40
–60
–80
Figure 57. Default Filter Frequency Response (2.5 MHz ODR)
0
0
500
FREQUENCY (kHz)
1000
–0.1dB FREQUENCY = 1.004MHz
PASS-BAND RIPPLE = 0.05dB
–3dB FREQUENCY = 1.06MHz
1500
STOP BAND = 1.25MHz
2000
2500