EMI Filter Transient - Amphenol Aerospace

AmphenolAerospaceImpedance Matching Formula(Your System to a 50 Ohm System)38999IIIHDDualokIIISJTAccessoriesAquaconHerm/SealPCBHighSpeedFiberOpticsContactsConnectorsCablesThe following formula and example are offered in order todeter mine the expected filter performance in an impedancesystem other than 50 ohms.With the attenuation expressed in 50 ohms and the transferimpedance curve shown in Figure 1 below, a designer can relatethe expressed attenuation to the input and output imped ance oftheir circuit.Example:(1) Noise is 40dB above specification level at 100 MHz(2) Output and input impedance are 10 and 100 ohmsrespectively(3) Amphenol ® VHF 7000 pf filter has a 65 dB minimumattenuation at 100 MHz and +25°CFormula (Taken from Figure 1):1.4 x 10 -2 ohm = transfer impedancefor 65 dB in a 50 ohm systemAtten (dB) = 20 log 101 +Z S= source impedance (output)Z L= load impedance (input)Z 12= transfer impedanceAtten = filter performance in a system other than 50 ohms10(100)Atten (dB) = 20 log 101 + 1.4 x 10 –2 (10 + 100)Attenuation = 56.3dBZ SZ LZ 12(Z S+ Z L)In this case, the 7000 pf VHF filter will give 56.3 dB which is16.3dB below the desired reduction in noise (40dB) as statedin the above problem.EMI FilterTransient140Attenuation vs Transfer Impedance in 50 Ohm System26482Matrix 212083723 IIIMatrix|Pyle5015 26500PyleOptions Back- 22992Others Shells Class L Crimp RearReleaseMatrixAttenuation - dB10080604020010-410-310-210-110-0101Transfer Impedance - Z 12 OhmsFigure 1276Contact Amphenol Aerospace for more information at 800-678-0141 or Filterapps@amphenol-aao.com • www.amphenol-aerospace.com