Chapter 2
BNC-2080 Board
© National Instruments Corporation
2-17
BNC-208X Series User Manual
Channel 9
(-in)
Channel 1
(+in)
BNC Connector
R4
R11
R15
R21
R3
R20
C2
19.8-k
1
Resistor
Channel 9
(-in {Case})
Channel 1
(+in {Center})
F
G
E
To
Input
Multiplexer
Input Schematic for
ACH1
BNC Connector
1-
µ
F Capacitor
R3 = 19.8 k
1
R20 = 19.8 k
1
C2 = 1
µ
F
+
-
A
B
C
D
E
F
G
Figure 2-13. Lowpass Filter on Differential Channel 1
Building Highpass Filters
Simple, R-C highpass filters are easily installed in the BNC-2080 board on any differential input
channel. The filters are useful for accurate high-frequency measurement and low-frequency noise
rejection. By substituting resistance and capacitance values into the following formula, hereafter
referred to as Formula 2-2, you can calculate a simple, one-pole R-C filter to have a -3-dB point fc:
fc =
1
(2
/
RC)
(Formula
2-2)
The frequency response rolls off at a rate of -20 dB per decade decrease thereafter. A Bode plot of
the amplitude versus normalized frequency is shown in Figure 2-14.
