BNC-2080 Board
Chapter 2
BNC-208X Series User Manual
2-16
© National Instruments Corporation
Channel 9
(-in)
Channel 1
(+in)
BNC Connector
R4
R11
R15
R21
R3
R20
C2
19.8-k
Ω
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
Ω
R20 = 19.8 k
Ω
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
π
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.