ADS5294 Datasheet, PDF (43/67 Pages) Texas Instruments – Octal Channel 14-Bit, 80 MSPS High-SNR and Low-Power ADC

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ADS5294
SLAS776B – NOVEMBER 2011 – REVISED JULY 2012
Coefficient Sets 1 and 2 are the most appropriate when Decimation by a factor of 2 is required, whereas
Coefficient Sets 3,4,5,6 are appropriate when Decimation by a factor of 4 is desired. The computation rate of the
filter output can be independently set using the bits FILTERn_RATE<2:0>. The settings are shown in Table 5.
Table 5. Digital Filters
DECIMATION
TYPE OF FILTER
Decimate by 2
Decimate by 4
Decimate by 2
Decimate by 4
Decimate by 8
Bypass decimation
Built-in low-pass odd-tap filter (pass band = 0 to f_S/4)
Built-in high-pass odd-tap filter (pass band = 0 to f_S/4)
Built-in low-pass even-tap filter (pass band = 0 to f_S/8)
Built-in first band pass even tap filter(pass band = f_S/8 to f_S/4)
Built-in second band pass even tap filter(pass band = f_S/4 to 3
f_S/8)
Built-in high pass odd tap filter (pass band = 3 f_S/8 to f_S/2)
Custom filter (user programmablecoefficients)
Custom filter (user programmablecoefficients)
Custom filter (user programmablecoefficients)
Custom filter (user programmablecoefficients)
<DATA
RATE>
001
001
010
010
010
010
001
010
011
FILTERn
RATE>
000
000
001
001
001
001
000
001
100
<FILTERn
COEFF SET>
<ODD TAP>
000
1
001
1
010
0
011
0
100
0
101
1
000
0 and 1
000
0 and 1
000
0 and 1
0 and 1
<USE
FILTER
CHn>
1
1
1
1
1
1
1
1
1
1
<EN CUSTOM
FILT>
0
0
0
0
0
0
1
1
1
1
The choice of the odd/even tap setting, filter coefficient set and the filter rate uniquely determines the filter to be
used. In addition to the preset filter coefficients, the coefficients for each of the eight filter channels can be
programmed by the user. Each of the eight channels has 12 programmable coefficients, each 12-bit long. The 96
registers with addresses from 5A (Hex) to B9 (Hex) are used to program these 8 sets of 12 programmable
coefficients. Registers 5A to 65 are used to program the 1^st filter, with the 1^st coefficient occupying the bits
D11..D0 of register 5A, the 2^nd coefficient occupying the bits D11..D0 of register 5B, and so on. Similarly
registers 66(Hex) to 71(Hex) are used to program the 2^nd filter, and so on.
When programming the filter coefficients, the D15 bit of each of the 12 registers corresponding to that filter
should be set to ‘1’. If the D15 bit of these 12 registers is set to ‘0’, then the preset coefficient (as programmed by
FILTERn_COEFF_SET<2:0>) is used even if the bits D11..D0 get programmed. By setting or not setting the D15
bits of individual filter channels to ‘1’, some filters can be made to operate with preset coefficient sets, and some
others can be made to simultaneously operate with programmed coefficient sets.
HIGH PASS FILTER
ADDR.
(HEX)
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
NAME
2E
XXXX
HPF_corner_CH1
2E
X
HPF_EN_CH1
2F
XXXX
HPF_corner_CH2
2F
X
HPF_EN_CH2
30
XXXX
HPF_corner_CH3
30
X
HPF_EN_CH3
31
XXXX
HPF_corner_CH4
31
X
HPF_EN_CH4
32
XXXX
HPF_corner_CH5
32
X
HPF_EN_CH5
33
XXXX
HPF_corner_CH6
33
X
HPF_EN_CH6
34
XXXX
HPF_corner_CH7
34
X
HPF_EN_CH7
35
XXXX
HPF_corner_CH8
35
X
HPF_EN_CH8
This group of registers controls the characteristics of a digital high pass transfer function applied to the output
data, useing Equation 3:
y(n)
=
2^k _[x(n)
2^k +1
-
x(n
-1)+y(n
-1)]
(3)
Copyright © 2011–2012, Texas Instruments Incorporated
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