124A

Build Your LC Filter
with the Coilcraft
Reference Design
LC Filter Reference Design uses off-the-shelf components
LC filters are widely used in many applications to provide
a variety of frequency characteristics. While passive filters
may seem simpler in concept than active filters, design
and performance verification can still be a time consuming process, involving some trial and error. To simplify
LC filter design, especially high order filters that require
more complex computations, Coilcraft has created LC
filter reference design evaluation modules, including 3rd
order Butterworth low-pass and high-pass, as well as 7th
order elliptic. These modules demonstrate the high performance that can be achieved using Coilcraft inductors
and standard capacitors.
LC Filters are classified as low-pass, high-pass, bandpass, and band-stop. They can be identified by their
particular frequency response characteristics, including
Butterworth, Chebyshev, Bessel, and Elliptic. Each has
certain advantages and disadvantages and represents
various trade-offs between the pass-band ripple and stopband attenuation.
Benefits of Coilcraft Reference Design
Free filter design programs are available that provide ideal
element component values that can be used when starting
an LC filter design. One such program, Design LC filter, is
available at http://www.wa4dsy.net/filter/filterdesign.html.
For example, to achieve a 3rd order low-pass LC filter
providing the cutoff frequency at 1200 MHz, the program
suggests the ideal model with component values L1,
L2 = 6.6 nH and C1 = 5.31 pF (see Figure 1). These
values can be used as a starting point for the real filter
design. However, without considering component and PCB
parasitics, they may not be very close to real-world performance, resulting in a time consuming process of tuning and
adjusting, particularly for the high cutoff frequency filters.
For a high performance design example including component parasitic effects and PCB board parasitic interactions
of the components with the circuit board, Coilcraft offers
3rd order Butterworth low-pass filter reference designs.
The Butterworth low-pass filter uses two 3.9 nH 0805HT
Series inductors and a 3.6 pF capacitor targeting a
1200 MHz cutoff frequency. The frequency response of
the filter measured with the LC components mounted on
a 25 mil thick ceramic substrate yields a cutoff frequency
of approximately 1100 MHz. The difference between the
calculated value and the real measurement reflects the
component parasitic effects and the circuit board effects.
On the other hand, simulating the design including the
inductor parasitics by using s-parameters predicts a cutoff
frequency of 1700 MHz (Figure 2), which is not particularly
close. This suggests the non-ideal PCB characteristics and
parasitic arising from the connection of the components
to the PCB are significant and must be included to make
the model complete. In any event, the reference design
measurements provide a handy, accurate, real-world
picture of filter performance
Third Order Butterworth Reference
Design (page 4)
The 3rd order Butterworth LC low-pass and high-pass
filters are two common types. The frequency response
of the Butterworth filter has the least pass-band ripple.
Figure 1.
Document 124A-1 Revised 04/21/16
Figure 2.
The inductors selected for 3rd order Butterworth reference designs are off-the-shelf Coilcraft 0805HT series.
These wirewound ceramic chip inductors are low profile
(only 0.035 inch high) and have a small footprint, offering
tremendous board space saving. The 0805HT has tight
tolerance at 2% to ensure that the required performance
is obtained. The designs feature 50 Ohm characteristic
impedance and less than 0.3 dB insertion loss.
The 3rd order low-pass filters reference design provides
a wide range of cut-off frequencies from 3 MHz to 3 GHz.
For 3-pole high-pass filter, 15 MHz to 900 MHz cutoff
frequencies could be obtained. User may simply order the
part number in the reference design BOM list to get the
closest component values for the design requirements.
The designer may modify or enhance the filter design
based on Coilcraft reference design (e.g., by using larger
inductors to achieve improved performance). Coilcraft offers a wide range of off-the-shelf inductors that designers
can choose from.
Frequency Response – 3 Pole Low-Pass Filters*
0
dB Attenuation (re: 50)
dB Attenuation (re: 50)
0
S3LP-156
S3LP-306
20
S3LP-606
40
60
80
S3LP-157
10
S3LP-807
20
30
40
10
100
1000
100
Frequency (MHz)
1000
10000
Frequency (MHz)
0
0
dB Attenuation (re: 50)
dB Attenuation (re: 50)
S3LP-507
S3LP-307
S3LP-707
10
S3LP-907
S3LP-128
20
30
40
S3LP-188
10
S3LP-218
20
S3LP-158
30
40
100
1000
Frequency (MHz)
10000
100
1000
10000
Frequency (MHz)
*Measured on Agilent/HP 8753D network analyzer (re: 50)
Document 124A-2 Revised 04/21/16
Frequency Response – 3 Pole High Pass Filters*
0
S3HP-306
20
dB Attenuation (re: 50)
dB Attenuation (re: 50)
0
S3HP-606
S3HP-156
40
60
S3HP-307
10
S3HP-157
S3HP-807
S3HP-507
20
30
40
80
1
10
100
10
100
1000
Frequency (MHz)
Frequency (MHz)
Seventh Order Elliptic Filter Reference
Design (page 5)
Compared to a Butterworth filter, elliptic filters have
equalized ripple in both the passband and the stop-band.
However, for the same order level, it has the fastest transition between passband and the stop-band. Coilcraft offers
7th order elliptic reference designs with less than 0.3 dB
insertion loss and 50-Ohm characteristic impedance. The
off-the-shelf selection of inductors is our 1812LS Series
ferrite chip inductor. The tolerance is as low as 5%. These
seventh order elliptic lowpass filters offer sharp roll-off rate
at 80 dB/dec and wide range of cutoff frequencies from
0.3 MHz to 500 MHz.
Summary
Typically, a passive LC filter design starts with calculations
and then a very iterative trial-and-error process.
Coilcraft LC filter reference designs can save time, effort
and cost for LC passive filter designers, allowing them to
better select the right components and achieve desired
performance. The reference designs included in this app
note include BOMs of standard off-the-shelf inductors
and capacitor values. For further discussion of the LC
filter design program and inductor models, refer to the
application note “Passive LC Filter Design and Analysis”.
0
0
10
10
20
20
Attenuation (dB)
Attenuation (dB)
Frequency Response – 7 Pole Filters*
30
40
P7LP-604
P7LP-304
50
60
0.1
1
60
Frequency (MHz)
0
0
10
20
20
30
P7LP-306
P7LP-606
40
P7LP-156
60
1
10
Frequency (MHz)
100
P7LP-507
P7LP-307
30
40
50
P7LP-157
60
70
70
80
P7LP-155
50
80
10
Attenuation (dB)
Attenuation (dB)
40
10
50
P7LP-305
30
70
70
80
P7LP-605
10
100
Frequency (MHz)
1000
80
100
1000
Frequency (MHz)
10000
*Measured on Agilent/HP 8753D network analyzer (re: 50)
Document 124A-3 Revised 04/21/16
Document 124A-4 Revised 04/21/16
–3 dB
cutoff
(MHz)
3
6
10
13
15
30
45
60
70
95
100
110
150
200
230
300
350
400
450
500
700
800
900
1000
1200
1500
1600
1800
2000
2600
3000
L1 part number
0805HT-R79TGLB
0805HT-R79TGLB
0805HT-R63TGLB
0805HT-R63TGLB
0805HT-R50TGLB
0805HT-R18TGLB
0805HT-R18TGLB
0805HT-R12TGLB
0805HT-R10TGLB
0805HT-72NTGLB
0805HT-68NTGLB
0805HT-68NTGLB
0805HT-68NTGLB
0805HT-33NTGLB
0805HT-33NTGLB
0805HT-33NTGLB
0805HT-18NTGLB
0805HT-17NTGLB
0805HT-18NTGLB
0805HT-18NTGLB
0805HT-8N2TGLB
0805HT-8N2TGLB
0805HT-4N7TGLB
0805HT-3N9TGLB
0805HT-3N9TGLB
0805HT-3N9TGLB
0805HT-2N2TJLB
0805HT-1N8TJLB
0805HT-1N8TJLB
0805HT-1N8TJLB
0805HT-1N8TJLB
L2 part number
0805HT-R79TGLB
0805HT-R79TGLB
0805HT-R63TGLB
0805HT-R63TGLB
0805HT-R50TGLB
0805HT-R18TGLB
0805HT-R18TGLB
0805HT-R12TGLB
0805HT-R10TGLB
0805HT-72NTGLB
0805HT-68NTGLB
0805HT-68NTGLB
0805HT-68NTGLB
0805HT-33NTGLB
0805HT-33NTGLB
0805HT-33NTGLB
0805HT-18NTGLB
0805HT-17NTGLB
0805HT-18NTGLB
0805HT-18NTGLB
0805HT-8N2TGLB
0805HT-8N2TGLB
0805HT-4N7TGLB
0805HT-3N9TGLB
0805HT-3N9TGLB
0805HT-3N9TGLB
0805HT-2N2TJLB
0805HT-1N8TJLB
0805HT-1N8TJLB
0805HT-1N8TJLB
0805HT-1N8TJLB
3-Pole Low Pass Filters
L1
(nH)
790 ±2%
790 ±2%
630 ±2%
630 ±2%
500 ±2%
180 ±2%
180 ±2%
120 ±2%
100 ±2%
72 ±2%
68 ±2%
68 ±2%
68 ±2%
33 ±2%
33 ±2%
33 ±2%
18 ±2%
17 ±2%
18 ±2%
18 ±2%
8.2 ±2%
8.2 ±2%
4.7 ±2%
3.9 ±2%
3.9 ±2%
3.9 ±2%
2.2 ±5%
1.8 ±5%
1.8 ±5%
1.8 ±5%
1.8 ±5%
L2
C1 ±2%
(nH)
(pF)
790 ±2%
2400
790 ±2%
1200
630 ±2%
680
630 ±2%
470
500 ±2%
390
180 ±2%
220
180 ±2%
120
120 ±2%
100
100 ±2%
91
72 ±2%
62
68 ±2%
56
68 ±2%
56
68 ±2%
33
33 ±2%
30
33 ±2%
24
33 ±2%
15
18 ±2%
15
17 ±2%
12
18 ±2%
10
18 ±2%
9.1
8.2 ±2%
6.8
8.2 ±2%
5.6
4.7 ±2%
5.6
3.9 ±2%
4.7
3.9 ±2%
3.6
3.9 ±2%
2.7
1.8 ±5%
2.7
1.8 ±5%
2.0
1.8 ±5%
1.5
1.8 ±5%
1.0
1.8 ±5%
0.5
Coilcraft
low pass filter
part number
S3LP305L
S3LP605L
S3LP106L
S3LP136L
S3LP156L
S3LP306L
S3LP456L
S3LP606L
S3LP706L
S3LP956L
S3LP107L
S3LP117L
S3LP157L
S3LP207L
S3LP237L
S3LP307L
S3LP357L
S3LP407L
S3LP457L
S3LP507L
S3LP707L
S3LP807L
S3LP907L
S3LP108L
S3LP128L
S3LP158L
S3LP168L
S3LP188L
S3LP218L
S3LP268L
S3LP308L
The S3LP and S3HP modules incorporate the components of this design into 1812-size
surface mount packages.
These low and high pass filter circuits serve a wide variety of filtering requirements. The
design features 3rd order Butterworth alignment, 50 Ohm characteristic impedance and
low insertion loss.
L1
C1
L2
Low pass filter
OUT
L1 part number
0805HT-R22TGLB
0805HT-R18TGLB
0805HT-68NTGLB
0805HT-39NTGLB
0805HT-27NTGLB
0805HT-15NTGLB
0805HT-6N8TGLB
0805HT-3N9TGLB
0805HT-3N9TGLB
0805HT-3N9TGLB
L1
±2%
(nH)
220
180
68
39
27
15
6.8
3.9
3.9
3.9
IN
C1
±2%
(pF)
330
68
56
39
20
6.8
5.6
4.5
3.0
2.2
C1
L1
C2
±2%
(pF)
390
68
56
39
20
6.8
5.6
4.5
3.0
2.2
C2
OUT
Coilcraft
high pass filter
part number
S3HP156L
S3HP306L
S3HP606L
S3HP107L
S3HP157L
S3HP307L
S3HP507L
S3HP707L
S3HP807L
S3HP907L
High pass filter
Document R124-1
Revised 04/15/14
All values are for reference only. Layout and substrate affect final performance.
3rd order Butterworth filter (refer to schematics). Ref. 50 Ohms.
Improved performance may be achieved by using other (typically larger) inductors.
Use the RF Inductor Finder tool to find alternatives.
Notes:
–3 dB
cutoff
(MHz)
15
30
60
100
150
300
500
700
800
900
3-Pole High Pass Filters
IN
Designing low- and high-pass filters using off-the shelf components
LC Filter Circuit Design
Document 124A-5 Revised 04/21/16
L1 part number
1812LS-333XJLB
1812LS-183XJLB
1812LS-183XJLB
1008LS-153XJLB
1812LS-123XJLB
1812LS-123XJLB
1812CS-103XJLB
1008CS-472XJLB
1008LS-682XJLB
1008LS-332XJLB
1008LS-332XJLB
1008CS-182XJLB
1008CS-152XJLB
1008CS-182XJLB
1008CS-222XJLB
1008CS-102XJLB
1008CS-102XJLB
1008CS-681XJLB
1008CS-911XJLB
1008CS-561XJLB
1008CS-331XJLB
1008CS-221XJLB
1008CS-151XJLB
1008CS-151XJLB
1008CS-121XJLB
1008CS-121XJLB
1008CS-101XJLB
1008CS-620XJLB
1008CS-470XJLB
1008CS-330XJLB
1008CS-150XJLB
1008CS-270XJLB
1008CS-180XJLB
1008CS-100XJLB
L2 part number
1812LS-333XJLB
1812LS-223XJLB
1812LS-183XJLB
1008LS-153XJLB
1812LS-123XJLB
1812LS-123XJLB
1812CS-103XJLB
1008CS-472XJLB
1008LS-682XJLB
1008LS-332XJLB
1008LS-332XJLB
1008CS-182XJLB
1008CS-621XJLB
1008CS-222XJLB
1008CS-272XJLB
1008CS-102XJLB
1008CS-102XJLB
1008CS-681XJLB
1008CS-911XJLB
1008CS-561XJLB
1008CS-221XJLB
1008CS-181XJLB
1008CS-151XJLB
1008CS-151XJLB
1008CS-121XJLB
1008CS-121XJLB
1008CS-101XJLB
1008CS-680XJLB
1008CS-470XJLB
1008CS-330XJLB
1008CS-120XJLB
1008CS-180XJLB
1008CS-120XJLB
0805CS-060XJLB
L3 part number
1812LS-273XJLB
1812LS-183XJLB
1812LS-153XJLB
1008LS-153XJLB
1812LS-153XJLB
1812LS-103XJLB
1812CS-822XJLB
1008CS-472XJLB
1008LS-562XJLB
1008LS-332XJLB
1008LS-272XJLB
1008CS-182XJLB
1008CS-821XJLB
1008CS-182XJLB
1008CS-222XJLB
1008CS-102XJLB
1008CS-102XJLB
1008CS-561XJLB
1008CS-911XJLB
1008CS-471XJLB
1008CS-221XJLB
1008CS-181XJLB
1008CS-121XJLB
1008LS-121XJLB
1008CS-121XJLB
1008LS-101XJLB
1008CS-850XJLB
1008CS-500XJLB
1008CS-390XJLB
1008CS-330XJLB
1008CS-270XJLB
1008CS-180XJLB
1008CS-120XJLB
0805CS-060XJLB
L1
±5%
(nH)
33000
18000
18000
15000
12000
12000
10000
4700
6800
3300
3300
1800
1500
1800
2200
1000
1000
680
910
560
330
220
150
150
120
120
100
62
47
33
15
27
18
10
L2
±5%
(nH)
33000
22000
18000
15000
12000
12000
10000
4700
6800
3300
3300
1800
620
2200
2700
1000
1000
680
910
560
220
180
150
150
120
120
100
68
47
33
12
18
12
6.8
L3
±5%
(nH)
27000
18000
15000
15000
15000
10000
8200
4700
5600
3300
2700
1800
820
1800
2200
1000
1000
560
910
470
220
180
120
120
120
100
85
50
39
33
27
18
12
6.8
C1
C2
±5%
±5%
(pF)
(pF)
6800
510
3300
270
3300
270
3300
240
2200
150
2200
200
1800
160
1500
110
1200
100
1200
100
50
620
620
50
600
210
390
30
240
200
220
3000
200
16
130
10
120
6
100
10
100
15
47
8.2
30
2.7
27
2.2
20
1.6
20
1.6
20
1.8
100
1
8.2
1
8.2
1
1.2
10
8.2
1.5
6.5
1
4.7
1
IN
Allvalues
values are
are for
for reference
reference only. Layout and
All
and substrate
substrate affect
affectfinal
finalperformance.
performance.
7thorder
orderelliptic
elliptic filter
filter (refer to schematics).
7th
schematics). Ref.
Ref.50
50 Ohms.
Ohms.
Use0805
0805NPO/COG
NPO/COG capacitors.
capacitors. Higher cut-off frequencies
Use
frequencies may
mayrequire
requiretighter
tightertolerance.
tolerance.
Improvedperformance
performance may
may be achieved by using
toto
find
alternatives.
Improved
using other
other (typically
(typicallylarger)
larger)inductors.
inductors.Use
Usethe
theRF
RFInductor
InductorFinder
Findertool
tool
find
alternatives.
Notes:
Notes:
–3 dB
cutoff
(MHz)
0.30
0.50
0.60
0.62
0.80
0.90
1.0
1.3
1.5
2.0
3.0
4.2
4.5
5.0
6.0
9.0
10
15
17
20
30
45
60
70
88
90
100
150
200
220
250
300
400
500
7-Pole Low Pass Filters
The P7LP modules incorporate the components of this design.
These low-pass filter circuits serve a wide variety of filtering requirements. The design features 7th order elliptic alignment, 50 Ohm characteristic impedance and low insertion loss.
Designing low- and high-pass filters using off-the shelf components
LC Filter Circuit Design
C3
C4
±5%
(pF)
3300
1800
1800
1000
750
820
680
620
510
510
300
300
1200
130
90
120
100
75
27
39
75
47
24
1000
10
10
7.5
4.7
3
3
17
7
5.1
6.2
C5
C6
±5%
(pF)
1500
910
910
910
560
6800
560
1800
360
360
180
180
800
110
75
100
600
36
27
3000
56
3000
9.1
7.5
6.2
6.2
6
3.3
2.2
2.2
2.7
5.1
3.9
4.3
L3
C6
OUT
Revised 04/15/14
C7
Coilcraft
±5%
low pass filter
(pF)
part number
5600
P7LP-304L
2200
P7LP-504L
2200
P7LP-604L
2200
P7LP-624L
1800
P7LP-804L
1800
P7LP-904L
1500
P7LP-105L
1500
P7LP-135L
1000
P7LP-155L
1000
P7LP-205L
510
P7LP-305L
50
P7LP-425L
250
P7LP-455L
300
P7LP-505L
220
P7LP-605L
200
P7LP-905L
160
P7LP-106L
100
P7LP-156L
120
P7LP-176L
100
P7LP-206L
70
P7LP-306L
3000
P7LP-456L
27
P7LP-606L
200
P7LP-706L
18
P7LP-886L
18
P7LP-906L
16
P7LP-107L
10
P7LP-157L
6.8
P7LP-207L
6.8
P7LP-227L
6
P7LP-257L
5.6
P7LP-307L
4.7
P7LP-407L
3
P7LP-507L
C7
Document R124-2
C5
±5%
(pF)
15000
6800
6800
6800
5600
5600
4700
1800
3300
3300
1500
1200
560
910
560
560
510
300
180
270
120
56
600
600
47
47
47
30
200
200
10
9.5
8.2
4.3
L2
L1
C3
±5%
(pF)
15000
6800
6800
6800
5600
5600
4700
1800
3300
3300
1500
1200
710
910
620
560
510
330
180
270
140
68
68
600
50
50
47
30
200
200
8.2
10
9.1
5.6
C1
C4
C2
Similar pages