AD7763 Analog Devices, AD7763 Datasheet - Page 26

• Manufacturer Part Number: AD7763
• Description: 24-Bit, 625 kSPS, 109 dB Sigma-Delta ADC with On-Chip Buffers, Serial Interface
• Manufacturer: Analog Devices

Specifications of AD7763

• Resolution (bits): 24bit
• # Chan: 1
• Sample Rate: 40MSPS
• Interface: I2S,Ser
• Analog Input Type: Diff-Bip
• Ain Range: 4 V p-p,6.5 V p-p
• Adc Architecture: Sigma-Delta
• Pkg Type: QFP

AD7763
EXAMPLE FILTER DOWNLOAD
The following is an example of downloading a short, user-defined
filter with 24 taps. The frequency response is shown in Figure 38.
The coefficients for the filter in Table 14 are shown from the center
of symmetry outward; that is, Coefficient 1 is the coefficient at the
center of symmetry. The raw coefficients were generated using a
commercial filter design tool and scaled appropriately so their
sum equals 67108863 (0x3FF FFFF).
Table 14. 24-Tap FIR Coefficients
Coefficient
1
2
3
4
5
6
7
8
9
10
11
12
–10
–20
–30
–40
–50
–60
–70
–80
10
0
0
Figure 38. 24-Tap FIR Frequency Response
100
Raw
+0.365481974
+0.201339905
+0.009636604
−0.075708848
−0.042856209
+0.019944246
+0.036437914
+0.007592007
−0.021556583
−0.024888355
−0.012379538
−0.001905756
200
FREQUENCY (kHz)
300
400
Scaled
[phone]
[phone]
+1402406
−11017834
−6236822
+2902466
+5302774
+1104856
−3137108
−3621978
−1801582
−277343
500
600
Rev. A | Page 26 of 32
Table 15 shows the 32-bit word (as per the format shown in the
Downloading a User-Defined Filter section) in hexadecimal for
each of the coefficients that must be written to the AD7763 to
realize this filter. The table is also split into the bytes that are all
summed to produce the checksum. The checksum generated
from these coefficients is 0x0E6B.
Table 15. Filter Hex Values
Coefficient
1
2
3
4
5
6
7
8
9
10
11
12
1
Table 16 lists in hexadecimal format the sequence of 32-bit
words the user writes to the AD7763 to set up the ADC and
download this filter, assuming selection of an output data rate
of 625 kHz.
Table 16.
Word
0x0001807A
0x032B9688
0x01BF183C
…
0x04043B5F
0x00000E6B
0x0001087A
1
All values of words listed are with reference to writing to one device only
(ALL = 0) with Address 000 (as assigned to the device using the ADR[2:0]
pins).
All values of words listed are with reference to writing to one device only
(ALL = 0) with Address 000 (as assigned to the device using the ADR[2:0]
pins).
1
32-Bit Word Written to Download Coefficient
Byte 1
03
01
00
04
04
00
00
00
04
04
04
04
Description
Address of Control Register 1. Control register
data. DL filter, set filter length = 24, set output
data rate = 625 kHz.
First coefficient.
Second coefficient.
Other coefficients.
Twelfth (final) coefficient.
Checksum. Wait (0.5 × t
coefficients) for AD7763 to fill remaining unused
coefficients with 0s.
Address of Control Register. Control register data.
Set read status and maintain filter length and
decimation settings. Read contents of status
register. Check Bit 7 (DL_OK) to determine that
the filter downloaded correctly.
Byte 2
2B
BF
15
A8
5F
2C
50
10
2F
37
1B
04
1
ICLK
Byte 3
96
18
66
1E
2A
49
E9
DB
DE
44
7D
3B
× number of unused
Byte 4
88
3C
26
6A
96
C2
F6
D8
54
5A
6E
5F