3-6
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Chapter 3
Analog Output Waveforms
Selecting Components for Lowpass Filtering
To determine the value of the components in the circuit, fix
R
(10 k
Ω
is reasonable) and isolate
C
from Equation 3-1 as follows:
(3-2)
The cut-off frequency in Equation 3-2 is
f
c
.
For best results, choose a resistor that has the following characteristics:
•
Low wattage of approximately 0.125 W
•
Precision of at least 5%
•
Temperature stability
•
Tolerance of 5%
•
AXL package (suggested)
•
Carbon or metal film (suggested)
Choose a capacitor that has the following suggested characteristics:
•
AXL or RDL package
•
Tolerance of 20%
•
Maximum voltage of at least 25 V
Adding Components for Lowpass Smoothing Filters on
Analog Output Signals
Using the circuit shown in Figure 3-8, you can use a two-component circuit to build a simple RC
filter with analog output. To build a lowpass filter for analog output, put a resistor in position A
and a capacitor in position B, as shown in Figure 3-9.
The SCB-68A ships with a surface mount 0
Ω
resistor in the A position. You
must
remove the
resistor to use the position. Refer to Table 3-1 for component positions for both analog output
channels.
C
1
2
π
Rfc
---------------
=
