Datasheet

20
0
20
40
60
80
100
-
-
-
-
-
-
-
120
140
Magnitude(dB)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
NormalizedFrequency(f /f )
IN DATA
0.000010
05
0
05
10
15
20
25
30
35
40
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
-
-
-
-
-
-
-
-
Magnitude(dB)
0 0.05 0.10 0.15 0.20 0.45
NormalizedFrequency(f /f )
IN DATA
0.25 0.30 0.35 0.40
2
0
2
4
6
8
10
-
-
-
-
-
Magnitude(dB)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
NormalizedFrequency(f /f )
IN DATA
ADS1675
www.ti.com SBAS416D –DECEMBER 2008–REVISED AUGUST 2010
Phase Response
The Low-Latency filter uses a multiple-stage,
linear-phase digital filter. Linear phase filters exhibit
constant delay time versus input frequency (also
know as constant group delay). This feature of linear
phase filters means that the time delay from any
instant of the input signal to the corresponding same
instant of the output data is constant and independent
of the input signal frequency. This behavior results in
essentially zero phase error when measuring
multi-tone signals.
WIDE-BANDWIDTH FILTER
The Wide-Bandwidth (WB) filter is well-suited for
measuring high-frequency ac signals. This digital filter
Figure 43. Frequency Response of
offers excellent passband and stop band
Wide-Bandwidth Filter
characteristics.
blank
The DRATE[2:0] digital input pins select from the four
data rates available with the WB filter, as shown in
Table 6. Note that the START pin must be strobed
after a change to the data rate. If a conversion is in
process during a data rate change, the output data
for that conversion are not valid and should be
discarded.
While using the Wide-Bandwidth filter path, the
LL_CONFIG pin must be set to logic high. Setting
LL_CONFIG low forces the ADS1675 to switch to a
low-latency filter path, overriding the FPATH pin.
Table 6. Wide-Bandwidth Data Rates
DATA –3dB
DRATE RATE SETTLING TIME, BANDWIDTH
[2:0] (kSPS) t
SETTLE-LL
(kHz)
Figure 44. Passband Response for
000 125 439.44ms 14062t
CLK
59.375
Wide-Bandwidth Filter
001 250 219.81ms 7074t
CLK
118.75
010 500 110.00ms 3520t
CLK
237.5
011 1000 55.04ms 1763t
CLK
475
100 2000 27.52ms 2642t
LSCLK
950
101 4000 13.79ms 1324t
LSCLK
1900
1. The input signal aliases when its frequency
exceeds f
DATA
/2, in accordance with the Nyquist
theorem.
Frequency Response
Figure 43 shows the frequency response for the
Wide-Bandwidth filter path normalized to the output
data rate, f
DATA
. Figure 44 shows the passband ripple,
and the transition from passband to stop band is
illustrated in Figure 45. These three plots are valid for
all of the data rates available on the ADS1675.
Figure 45. Transition Band Response for
Simply substitute the selected data rate to express
Wide-Bandwidth Filter
the x-axis in absolute frequency.
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