AD7760BSVZ Analog Devices Inc, AD7760BSVZ Datasheet - Page 31

• 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

DOWNLOADING A USER-DEFINED FILTER
As previously mentioned, the filter coefficients are 27 bits in
length—one sign and 26 magnitude bits. Because the AD7760
has a 16-bit parallel bus, the coefficients are padded with 5 MSB
0s to generate a 32-bit word, split into two 16-bit words for
downloading. The first 16-bit word for each coefficient becomes
(00000, sign bit, Magnitude [25:16]), whereas the second word
becomes (Magnitude [15:0]). To ensure that a filter is downloaded
correctly, a checksum must also be generated and then downloaded
following the final coefficient. The checksum is a 16-bit word
generated by splitting each 32-bit word into four bytes and
summing the bytes from all coefficients up to a maximum of
192 bytes (48 coefficients × four bytes). The same checksum
is generated internally in the AD7760 and compared with the
downloaded checksum. The DL_OK bit in the status register is
set if these two checksums agree.
To download a user filter
1.
2.
3.
4.
5.
6.
Note that because the user coefficients are stored in RAM, they
are cleared after a RESET operation or a loss of power.
Table 11. Filter Length Values
FLEN [3:0]
0000
0001
0011
0101
0111
1001
1011
1101
1111
Write to Control Register 1, setting the DL_FILT bit and
the correct filter length bits corresponding to the length of
the filter to be downloaded (see Table 11).
Write the first half of the current coefficient data
(00000, sign bit, Magnitude [25:16]). The first coefficient
to be written must be the one adjacent to the point of filter
symmetry.
Write the second half of the current coefficient data
(Magnitude [15:0]).
Repeat Step 2 and Step 3 for each coefficient.
Write the 16-bit checksum.
Use the following methods to verify that the filter coefficients
are downloaded correctly:
a.
b.
Read the status register, checking the DL_OK bit.
Read data and observe the status of the DL_OK bit.
Number of Coefficients
Default
6
12
18
24
30
36
42
48
Filter Length
Default
12
24
36
48
60
72
84
96
Rev. A | Page 31 of 36
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 58.
The coefficients for the filter are listed in Table 12 and are
shown from the center of symmetry outwards. The raw
coefficients were generated using a commercial filter design
tool and were scaled appropriately so that their sum equals
67,108,863 (0x3FF FFFF).
Table 12. 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 58. 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
53188232
29300796
1402406
−11017834
−6236822
2902466
5302774
1104856
−3137108
−3621978
−1801582
−277343
500
AD7760
6
00