Datasheet

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SBAS306F − NOVEMBER 2004 − REVISED OCTOBER 2007
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24
0
−
1
−
2
−
3
−
4
−
5
−
6
−
7
−
8
−
9
−
10
Normalized Input Frequency (f
IN
/f
DATA
)
Amplitude (dB)
0.45 0.47 0.49 0.51 0.53 0.55
Figure 60. Transition Band Response for
High-Resolution Mode
20
0
−
20
−
40
−
60
−
80
−
100
−
120
−
140
−
160
Gain (dB)
Normalized Input Frequency (f
IN
/f
DATA
)
0 32 64 96 128
Figure 61. Frequency Response out to f
MOD
for
High-Resolution Mode
Table 8. Antialiasing Filter Order Image Rejection
ANTIALIASING
IMAGE REJECTION (dB)
(f
−3dB
at f
DATA
)
ANTIALIASING
FILTER ORDER
HS, LP HR
1 39 45
2 75 87
3 111 129
PHASE RESPONSE
The ADS1271 incorporates a multiple stage, linear phase
digital filter. Linear phase filters exhibit constant delay time
versus input frequency (constant group delay). This
means the time delay from any instant of the input signal
to the same instant of the output data is constant and is
independent of input signal frequency. This behavior
results in essentially zero phase errors when analyzing
multi-tone signals.
SETTLING TIME
As with frequency and phase response, the digital filter
also determines settling time. Figure 62 shows the output
settling behavior after a step change on the analog inputs
normalized to conversion periods. The X axis is given in
units of conversion. Note that after the step change on the
input occurs, the output data changes very little prior to 30
conversion periods. The output data is fully settled after 76
conversion periods for High-Speed and Low-Power
modes, and 78 conversions for High-Resolution mode.
100
0
% Settling
Conversions (1/f
DATA
)
02010 4030 6050 8070
Fully Settled Data
at 76 Conversions
(78 Conversions for
High−Resolution mode)
Initial Value
Final Value
Figure 62. Settling Time for All Power Modes