Non-Ideal Behavior of Components

Transcription

1 Non-Ideal Behavior of Components Todd H. Hubing Dept. of Electrical and Computer Engineering Clemson, University Clemson, SC USA Telephone:

2 Circuit Schematics Global EMC University 2007 IEEE International Symposium on EMC 2

3 Resistors Global EMC University 2007 IEEE International Symposium on EMC 3

4 Resistance R = l σ A ohms Global EMC University 2007 IEEE International Symposium on EMC 4

5 Quiz Question The D.C. resistance of a 5-cm trace on a printed circuit board is, a.) about 100 ohms b.) about 100 milliohms c.) less than a milliohm Global EMC University 2007 IEEE International Symposium on EMC 5

6 DC Resistance of a Printed Circuit Board Trace Trace length = 5 cm Trace width = 0.25 mm Trace thickness = mm σ cu = 5.7 x 10 7 S/m. 0.05m R = = 0.10 ohms ( S / m )( 0.25x10 m )( 0.034x10 m ) Global EMC University 2007 IEEE International Symposium on EMC 6

7 Skin Depth High-frequency electric fields and currents decay exponentially with distance from the surface of a good conductor. J ( x) = J S e x πfμσ Global EMC University 2007 IEEE International Symposium on EMC 7

8 Skin Depth δ = 1 π f μσ meters Global EMC University 2007 IEEE International Symposium on EMC 8

9 Resistance per unit length of a cable At 60 Hz δ 60Hz 1 = = 8.6 mm π 7 7 ( 60)( 4π 10 )( ) 1 1 Rinnerconductorat60Hz = = = 22.3m Ω /m 2 σ A ( ) π ( ) 1 1 Routerconductorat60Hz = = = 5.6 m Ω / m σ A ( ) π ( )( ) total = = 28 m Ω / m Global EMC University 2007 IEEE International Symposium on EMC 9

10 Resistance per unit length of a cable At 100 MHz δ 100 MHz 1 = = mm π ( 10 )( 4π 10 )( ) 1 1 Rinnerconductorat100MHz = = = 832m Ω /m σ A ( ) π ( )( ) 1 1 Routerconductorat100MHz = = = 85m Ω /m σ A ( ) π ( )( ) total = = 917 m Ω / m Global EMC University 2007 IEEE International Symposium on EMC 10

11 Capacitors Global EMC University 2007 IEEE International Symposium on EMC 11

12 Capacitance C = Q V farads. Q E = 0 2 a 4πε0r < < r r r r volts/m. Q Q 1 1 4πε0r 4πε0 ra rb b 0 0 Vab = dr = volts. r 2 a b C ab Q 4πε 0 0 = = Vab 1 1 r a r b farads. Global EMC University 2007 IEEE International Symposium on EMC 12

13 Absolute Capacitance Cabs = limcab = 4πε 0ra farads. b Global EMC University 2007 IEEE International Symposium on EMC 13

14 Self and Mutual Capacitance Global EMC University 2007 IEEE International Symposium on EMC 14

15 Self and Mutual Capacitance Global EMC University 2007 IEEE International Symposium on EMC 15

16 Inductors Global EMC University 2007 IEEE International Symposium on EMC 16

17 Inductance Inductance is a property of current loops! Ψ = S B ds webers L Ψ = I henries Global EMC University 2007 IEEE International Symposium on EMC 17

18 Inductance L circle N 2 8R Rμ ln a 2.0 henrys L square loop w w N 2 2μ 0 ln π a henrys Global EMC University 2007 IEEE International Symposium on EMC 18

19 Quiz Question The inductance of a 2-cm wide, 10-cm long ground strap is, a.) about 10 nanohenries b.) about 100 nanohenries c.) undefined Global EMC University 2007 IEEE International Symposium on EMC 19

20 Loop Inductances Global EMC University 2007 IEEE International Symposium on EMC 20

21 Mutual Inductance L 21 Ψ = I 21 1 henries. Global EMC University 2007 IEEE International Symposium on EMC 21

22 Partial Inductance L L L Ψ = I = S Bids I 1 1 henries. ( A ) henries. ids L 12 L 11 1 A1 dl S = = i μi henries A1 = 1 dl / I1 I 4π R 1 webers m L21 μ dl idl 4π R = 1 2 henries Useful for computer modeling. Not useful for estimating inductance. L ij μ = 4 where I J π i = 0 i = 0 l ij l = ij segment i segment j dl idl i R ij j Global EMC University 2007 IEEE International Symposium on EMC 22

23 Partial Inductance (Branch Inductance) L loop = L trace + L via + L via + L plane Global EMC University 2007 IEEE International Symposium on EMC 23

24 Resistors Global EMC University 2007 IEEE International Symposium on EMC 24

25 Do Resistors Have Capacitance and Inductance? Global EMC University 2007 IEEE International Symposium on EMC 25

26 Impedance of a 50-Ohm Resistor 0.8 pf 20 nh 48 ohms 1000 Impedance in Ohms Frequency in MHz Global EMC University 2007 IEEE International Symposium on EMC 26

27 Types of Resistors Metal Film High precision, low cost Composite Medium precision, good transient immunity Wire Wound High power, high inductance Global EMC University 2007 IEEE International Symposium on EMC 27

28 Capacitors Global EMC University 2007 IEEE International Symposium on EMC 28

29 Do Capacitors Have Resistance and Inductance? μf 2 nh 15 mohms Global EMC University 2007 IEEE International Symposium on EMC 29

30 Impedance of a 0.01-μF Capacitor μf 2 nh 15 mohms 100 Impedance in Ohms Frequency in MHz Global EMC University 2007 IEEE International Symposium on EMC 30

31 What are ESR and ESL??!! Global EMC University 2007 IEEE International Symposium on EMC 31

32 SMT Capacitor Connection Inductance C = 3.4 nf B L = 5 nh BULK L = 2nH D C BULK = 1 μ F C = 10nF D Bare Board Board with decoupling MHz 1 MHz 10 MHz 100 MHz 1 GHz Global EMC University 2007 IEEE International Symposium on EMC 32

33 Types of Capacitors Ceramic Tantalum Other Electrolytic Mica Low cost, stable, good precision Polarized, good energy density Polarized, good energy density High-voltage applications Global EMC University 2007 IEEE International Symposium on EMC 33

34 Inductors Global EMC University 2007 IEEE International Symposium on EMC 34

35 Do Inductors Have Resistance and Capacitance? 160 pf 15 mohms 5 μh Global EMC University 2007 IEEE International Symposium on EMC 35

36 Impedance of a 5-μH Inductor 160 pf 15 mohms 5 μh 1000 Impedance in Ohms Frequency in MHz Global EMC University 2007 IEEE International Symposium on EMC 36

37 Types of Inductors Ferrite Core Air Core High inductance in small package Linear behavior under high-current conditions Common-mode Impedes common-mode currents while passing differential-mode currents. Global EMC University 2007 IEEE International Symposium on EMC 37

38 Ferrites Fair-Rite Global EMC University 2007 IEEE International Symposium on EMC 38

39 Non-Ideal Behavior of Active Devices Currents on the lead frame of an RDR memory module at the third harmonic of the clock frequency. Global EMC University 2007 IEEE International Symposium on EMC 39

40 Summary All components (when connected to a circuit) have resistance, capacitance and inductance. The behavior of a component at high frequencies is usually much different than the nominal (low-frequency) behavior. The inductance of a low-inductance device is generally determined by the connection and is not a property of the device itself. Global EMC University 2007 IEEE International Symposium on EMC 40