4-2
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Chapter 4
PFI 0 and Digital Input Measurements
Figure 4-2 shows the digital input channel configuration for PFI 0.
Figure 4-2.
Digital Input Channel Pad Configuration
The SCB-68A ships with a surface mount 0
Ω
resistor in the A position. You must remove the
resistor to use the position. If you remove your custom components from the A position, you
must reinstall a 0
Ω
resistor. The B position contains through hole pads that can be used for
two components to be connected in parallel.
Lowpass Filtering
Lowpass filters highly or completely attenuate signals with frequencies above the cut-off
frequency, or high-frequency stopband signals. Lowpass filters do not attenuate signals with
frequencies below the cut-off frequency, or low-frequency passband signals. Ideally, lowpass
filters have a phase shift that is linear with respect to frequency. This linear phase shift delays
signal components of all frequencies by a constant time, independent of frequency, thereby
preserving the overall shape of the signal.
In practice, lowpass filters subject input signals to a mathematical transfer function that
approximates the characteristics of an ideal filter. By analyzing the Bode Plot, or the plot that
represents the transfer function, you can determine the filter characteristics.
Figures 4-3 and 4-4 show the Bode Plots for the ideal filter and the real filter, respectively, and
indicate the attenuation of each transfer function.
45
11
44
S
C10
A
+
B
11
+
44
PFI 0
D GND
