Appendix B: Capacitor Coefficients for Lowpass Sallen-Key Filters

Robert A. Pease

Figure B-1: Schematic diagram of Sallen-Key filter for second order. Note that C2 is connected from the amplifier's + input to ground

Figure B-2: Schematic diagram of Sallen-Key filter for third order. Note that C2 is still connected from the amplifier's + input to ground. The capacitor C3 is connected from the nexus of R1 and R3 to ground. This circuit is used when odd orders are desired

Table B-1: Capacitor values for 0.01-dB Chebyshev lowpass Sallen-Key filters
Order (n)	C ₁	C ₂
2	1.4826	0.7042
4	1.4874 3.5920	1.1228 0.2985
6	1.8900 2.5820 7.0522	1.5249 0.5953 0.1486
8	2.3652 2.7894 4.1754 11.8920	1.9493 0.8196 0.3197 0.08672
(Refer to the circuits of Figures 6-10 and B-1, normalized to 1 ohm at f _3dB = 0.159 Hz; capacitors in Farads. Reprinted from Electronics, McGraw-Hill, Inc., Aug. 18, 1969.)

Table B-2: Capacitor Values for 0.1-dB Chebyshev lowpass Sallen-Key filters
Order (n)	C ₁	C ₂	C ₃
2	1.638	0.6955
3	6.653	0.1345	1.825
4	1.900 4.592	1.241 0.2410
5	4.446 6.810	0.3804 0.1580	2.520
6	2.553 3.487 9.531	1.776 0.4917 0.1110
7	5.175 4.546 12.73	0.5693 0.3331 0.08194	3.322
8	3.270 3.857 5.773 16.44	2.323 0.6890 0.2398 0.06292
9	6.194 4.678 7.170 20.64	0.7483 0.4655 0.1812 0.04980	4.161
10	4.011 4.447 5.603 8.727 25.32	2.877 0.8756 0.3353 0.1419 0.04037
(Refer to the circuits of Figures 6-10, 6-11, B-1, and B-2, normalized to 1 ohm at...

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Appendix B: Capacitor Coefficients for Lowpass Sallen-Key Filters

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