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