RF Electronics Chapter 7: RF Filters Page 211
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 7.1 shows the resulting circuit for a 7
th
order Lowpass filter with a 500 MHz cut-
off frequency. For the Butterworth filter, equations 7.1 and 7.2 are used to calculate the
required component values in the schematic. For the other filters, the component values
are calculated using a spreadsheet and the filter tables in Zverev.
Figure 7.1. Butterworth Lowpass Filter.
Figure 7.2. Butterworth Frequency Response.
Fc in MHz
Terminating Impedance in ohm
Seventh order Butterworth Low Pass Filter
For the Butterworth filter, the component values are calculated using the following equations:
C in pf
L in nH
Fc=500
R=50
C1=1e6*Sin(pi/14)/(pi*Fc*R)
pi=3.142
C1: 2.833
C3=1e6*Sin(5*pi/14)/(pi*Fc*R) C3: 11.47
C5=1e6*Sin(9*pi/14)/(pi*Fc*R) C5: 11.47
C7=1e6*Sin(13*pi/14)/(pi*Fc*R) C7: 2.833
L2=1e3*R*Sin(3*pi/14)/(pi*Fc) L2: 19.85
L4=1e3*R*Sin(7*pi/14)/(pi*Fc) L4: 31.83
L6=1e3*R*Sin(11*pi/14)/(pi*Fc) L6: 19.85
CAP
ID=C3
CAP
ID=C1
IND
ID=L6
IND
ID=L4
IND
ID=L2
PORT
P=2
Z=50 Ohm
PORT
P=1
Z=50 Ohm
CAP
ID=C7
CAP
ID=C5
RF Electronics: Design and Simulation
211 www.cadence.com/go/awr
