Chapter 5
Adding Components for Special Functions
©
National Instruments Corporation
5-11
SCB-68 Shielded Connector Block User Manual
Use Equation 5-3 to design a lowpass filter for a simple resistor and
capacitor circuit, where the values of the resistor and capacitor alone
determine
f
c
. In this equation,
G
is the DC gain and
s
represents the
frequency domain.
Selecting Components
To determine the value of the components in the circuit, fix
R
(10 k
Ω
is
reasonable) and isolate
C
from Equation 5-3 as follows:
(5-4)
The cut-off frequency in Equation 5-4 is
f
c
.
For best results, choose a resistor that has the following characteristics:
•
Low wattage of approximately 1/8 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
Using the circuit shown in Figure 5-11, you can use a two-component
circuit to build a simple RC filter with analog input, analog output, or
digital input. You can build a single-ended analog input RC filter with pads
F and B for one channel and pads G and D for the next channel. You can
build a differential analog input RC filter with pads F and E.
For TRIG1, you can use pads R1 and RC1. For AO, you can use R2 and
RC2 for DAC1OUT, and you can use R3 and RC3 for DAC0OUT.
C
1
2
π
Rfc
---------------
=
