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Chapter 4 Theory of Operation
SCXI-1141/1142/1143 User Manual 4-10 ni.com
Figure 4-7. Phase Error of the SCXI-1141/1142/1143 Module
The most common effect of phase nonlinearity is ringing in response to a
step input. As Figure 4-8 shows, the SCXI-1141 elliptic filter exhibits the
most overshoot and ringing and the SCXI-1142 Bessel filter has no
overshoot or ringing. The SCXI-1143 module Butterworth filter has a step
response that is a compromise between the SCXI-1141 module and the
SCXI-1142 module. The SCXI-1143 module filter has an overshoot, but it
has less ringing than the SCXI-1141. You should consider the step response
if the intended application is sensitive to overshoot or ringing. See
Table A-1, Settling Time with Respect to Cutoff Frequency, for detailed
settling specifications. Additionally, use care when selecting gain settings
to assure that the input signal plus any overshoot voltage result in an output
signal within the ±5 V range of the SCXI-1141/1142/1143 module.
0 0.5 1 1.5 2
–100
0
100
200
300
Bessel (1142)
Butterworth (1143)
Elliptic (1141)
Frequency (Normalized)
Phase Error (Degrees)