Current in IC During Logic Transitions (CMOS) V CC switch IC IC load driver V DC C L Z 0 , v p GND V CC V CC IC IC IC load IC load discharge charge driver driver V CC 0 V Z 0 , v p Z 0 , v p shoot-thru shoot- current GND thru GND logic 0-1 logic 1-0 current October 2007 Dr. Bruce Archambeault 34
Typical PCB Power Delivery DC/DC converter (Power source) electrolytic SMT capacitors capacitor GND V CC GND GND V CC V CC IC load GND GND IC driver V CC V CC GND V CC October 2007 Dr. Bruce Archambeault 35
Equivalent Circuit for Power Current Delivery to IC PCB connector wiring and wiring via interconnect capacitor L trace L ps leads L bulk L via IC load C planes V DC switch C bulk C SMT SMT DC/DC electrolytic capacitors V CC /GND converter capacitors plane October 2007 Dr. Bruce Archambeault 36
Traditional Analysis #1 • Use impedance of capacitors in parallel ESR 1 ESR 2 ESR 3 ESR 4 ESL 1 ESL 2 ESL 3 ESL 4 1uF 0. 1uF 0.01uF .001uF Impedance to IC No Effect of Distance Between Capacitors power/gnd pins and IC Included! October 2007 Dr. Bruce Archambeault 37
Traditional Impedance Calculation for Four Decoupling Capacitor Values 1000 100 .1uF .01uF .001uF .0001uF Impedance (ohms) 10 All in Parallel 1 0.1 0.01 1.00E+07 1.00E+08 1.00E+09 Frequency (Hz) October 2007 Dr. Bruce Archambeault 38
Traditional Analysis #2 • Calculate loop area – Traditional loop Inductance formulas – Which loop area? Which size conductor ESR 1 ESR 2 ESR 3 ESR 4 ESL 1 +L d1 ESL 2 +L d2 ESL 3 +L d3 ESL 4 +L d4 1uF 0. 1uF 0.01uF .001uF Impedance to IC power/gnd pins Over Estimates L and Ignores Distributed Capacitance October 2007 Dr. Bruce Archambeault 39
More Accurate Model Includes Distributed Capacitance Intentional Decoupling Capacitors Intentional Decoupling Capacitors IC Power Pin Distributed Distributed capacitors capacitors October 2007 Dr. Bruce Archambeault 40
Distributed Capacitance Schematic Intentional Intentional Distributed Capacitance Distributed Capacitance Capacitor Capacitor ESR ESR Loop L Loop L Note: L increases Note: L increases C apacitance C apacitance as distance from as distance from source increases source increases Source Source Source October 2007 Dr. Bruce Archambeault 41
Effect of Distributed Capacitance • Can NOT be calculated/estimated using traditional capacitance equation • Displacement current amplitude changes with position and distance from the source October 2007 Dr. Bruce Archambeault 42
Displacement Current 500 MHz via @450 mils from Source October 2007 Dr. Bruce Archambeault 43
Need to Find the Real Effect of Decoupling Capacitor Distance • Perfect decoupling capacitor is a via between planes • FDTD simulation to find the effect of shorting via distance from source • Vary spacing between planes, distance to via, frequency, etc October 2007 Dr. Bruce Archambeault 44
Impedance of Shorting Via vs. Frequency Four Via Case (20 mil Seperation Between Plates) 100 10 Impedance (ohms) 20mils 40mils 50mils 60mils 70mils 80mils 90mils 100mils 1 120mils 130mils 140mils 150mils 160mils 180mils 200mils 220mils 240mils 250mils 350mils 450mils 0.1 1.E+08 1.E+09 1.E+10 Frequency (Hz) October 2007 Dr. Bruce Archambeault 45
Impedance Result • Linear with frequency (on log scale) • Looks like an inductance only! • Consider this inductance an Apparent Inductance • Apparent inductance is constant with frequency October 2007 Dr. Bruce Archambeault 46
Apparent Inductance for One Shorting Via Case 20 mil Plate Separation 1.2 1 0.8 Inductance (nH) 0.6 50mils 0.4 110mils 120mils 200mils 250mils 0.2 350mils 450mils 0 1.E+08 1.E+09 1.E+1 Frequency (Hz) October 2007 Dr. Bruce Archambeault 47
Formulas to Predict Apparent Inductance = − + − + L ( 0 . 1336 s 0 . 0654 ) Ln ( dist ) ( 0 . 2609 s 0 . 2675 ) − one via = − + − + L ( 0 . 1307 s 0 . 0492 ) Ln ( dist ) ( 0 . 2948 s 0 . 1943 ) − two via = − + − + L ( 0 . 1242 s 0 . 0447 ) Ln ( dist ) ( 0 . 2848 s 0 . 1763 ) − three via = − + − + L ( 0 . 1192 s 0 . 0403 ) Ln ( dist ) ( 0 . 2774 s 0 . 1592 ) − four via s = separation between plates (mils/10) dist = distance to via October 2007 Dr. Bruce Archambeault 48
True Impedance for Decoupling Capacitor IC Capacitor Power Gnd L IC L cap L apparent L apparent ESR L cap + L IC Source Nominal Capacitance October 2007 Dr. Bruce Archambeault 49
Impedance Calculation with Apparent Inductance for Four Decoupling Capacitor Values 10 Case1 Cap Value Distance to Cap from IC Case 1 Case 2 Case 3 Case2 0.1 uF 800mils 1200mils 1500mils Case3 0.01 uF 600mils 900mils 1100mils Traditional Calculation 0.001uF 400mils 700mils 800mils 0.0001uF 200mils 400mils 400mils 1 Impedance (ohms) 0.1 0.01 1.E+07 1.E+08 1.E+09 Frequency (Hz) October 2007 Dr. Bruce Archambeault 50
Effect of Distributed Capacitance • Can NOT be calculated/estimated using traditional capacitance equation • Displacement current amplitude changes with position and distance from the source • Following examples use cavity resonance technique (EZ-PowerPlane) – Frequency Domain to compare to measurements – Time Domain using SPICE circuit from cavity resonance analysis October 2007 Dr. Bruce Archambeault 51
Parameters for Comparison to Measurements • Dielectric thickness = 35 mils • Dielectric constant = 4.5, Loss tan = 0.02 • Copper conductivity = 5.8 e7 S/m October 2007 Dr. Bruce Archambeault 52
Measured vs Model (MoM) S21 for 12" x 10" PC Power/gnd with 25 .01uF caps Position 8-to-1 0 No Caps - Measured -10 EZ-PP No Caps -20 S21 (dB) -30 -40 -50 1.0E+07 1.0E+08 1.0E+09 1.0E+10 Frequency (Hz) October 2007 Dr. Bruce Archambeault 53
Measured vs Model (EZ-PP) S21 for 12" x 10" PC Power/gnd with 25 .01uF caps Position 8-to-1 0.0 -10.0 -20.0 -30.0 -40.0 S21 (dB) -50.0 -60.0 Measured -70.0 EZ-PP 25 caps -80.0 -90.0 -100.0 1.0E+07 1.0E+08 1.0E+09 1.0E+10 Frequency (Hz) October 2007 Dr. Bruce Archambeault 54
Measured vs Model (EZ-PP) S21 for 12" x 10" PC Power/gnd with 95 .01uF caps Position 8-to-1 0.0 -10.0 -20.0 -30.0 -40.0 S21 (dB) -50.0 -60.0 95 Caps - Measured -70.0 95 Caps - EZ-PP -80.0 -90.0 -100.0 1.0E+07 1.0E+08 1.0E+09 1.0E+10 Frequency (Hz) October 2007 Dr. Bruce Archambeault 55
Impedance at Port #1 Single 0.01 uF Capacitor at Various Distances (35mil Dielectric) 30 20 10 Impedance (dBohms) 0 -10 -20 no caps 300 mils 500 mils 700 mils -30 1000 mils -40 1.0E+07 1.0E+08 1.0E+09 1.0E+10 October 2007 Dr. Bruce Archambeault 56 Frequency (Hz)
Z11 Phase Comparison as Capacitor distance Varies for 35 mils FR4 ESL = 0.5nH 2 1.5 1 0.5 Phase (rad) 0 -0.5 100 mils 200 mils -1 300 mils 400 mils 1000 mils -1.5 2000 mils -2 1.0E+06 1.0E+07 1.0E+08 1.0E+09 Frequency (Hz) October 2007 Dr. Bruce Archambeault 57
Impedance at Port #1 Single 0.01 uF Capacitor at Various Distances (10mil Dielectric) 20 10 0 no caps Impedance (dBohms) 300 mils -10 500 mils 700 mils 1000 mils -20 -30 -40 -50 1.0E+07 1.0E+08 1.0E+09 1.0E+10 October 2007 Dr. Bruce Archambeault 58 Frequency (Hz)
Cavity Resonance (EZ-PowerPlane) Equivalent Circuit for HSPICE L ij Port i Port j L ii L jj Port n N mni L mn G mn C 0 N mnj C 0 N 01i L 01 G 01 N 01j N 00i N 00j C 0 G 00 October 2007 Dr. Bruce Archambeault 59
Impedance Comparison (EZ-PP vs HSPICE) at Port #1 Single 0.01 uF Capacitor at Various Distances (10mil Dielectric) 20 10 0 Impedance (dBohms) -10 -20 300 mils -30 300 mils (HSPICE) 1000 mils 1000 mils (HSPICE) -40 -50 1.0E+07 1.0E+08 1.0E+09 1.0E+10 October 2007 Dr. Bruce Archambeault 60 Frequency (Hz)
Current Source Pulse for Simulated IC Power/GND 750 ps Rise/Fall 1.2 1 0.8 Current (amps) 0.6 0.4 0.2 0 -0.2 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (ns) October 2007 Dr. Bruce Archambeault 61
Time Domain Noise Voltage Across Simulated IC Power/GND Pin (1 amp) Single Capacitor (with 2 nH) at Various Distances (Fullwave Simulation) 2 1.5 750ps Rise, 35 mil planes,1uF @ 10mils 750ps Rise, 35 mil planes, 1uF @ 400mils 1 750ps Rise, 35 mil planes,1uF @ 800mils 750ps Rise, 35 mil planes,1uF @ 1200mils 750ps Rise, 35 mil planes,1uF @ 1600mils Level (volts) 0.5 0 -0.5 -1 -1.5 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (ns) October 2007 Dr. Bruce Archambeault 62
Time Domain Current through Capacitor From Simulated IC Power/GND (1 amp) Single Capacitor (with 2nH) at Various Distances 50 0 -50 -100 Current (milliamps) -150 -200 -250 750ps Rise, 35 mil planes,1uF @ 10mils 750ps Rise, 35 mil planes,1uF @ 400mils -300 750ps Rise, 35 mil planes,1uF @ 800mils 750ps Rise, 35 mil planes,1uF @ 1200mils 750ps Rise, 35 mil planes,1uF @ 1600mils -350 -400 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (ns) October 2007 Dr. Bruce Archambeault 63
Time Domain Noise Voltage Across Simulated IC Power/GND Pin (1 amp) Single Capacitor (with No L) at Various Distances 2 750ps Rise, 35 mil planes,1uF @ 10mils 750ps Rise, 35 mil planes,1uF @ 400mils 1.5 750ps Rise, 35 mil planes,1uF @ 800mils 750ps Rise, 35 mil planes,1uF @ 1200mils 750ps Rise, 35 mil planes,1uF @ 1600mils 1 0.5 Level (volts) 0 -0.5 -1 -1.5 -2 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (ns) October 2007 Dr. Bruce Archambeault 64
Time Domain Current through Capacitor From Simulated IC Power/GND (1 amp) Single Capacitor (with no L) at Various Distances 400 200 0 Current (milliamps) -200 -400 -600 750ps Rise, 35 mil planes,1uF @ 10mils 750ps Rise, 35 mil planes,1uF @ 10mils 750ps Rise, 35 mil planes,1uF @ 800mils -800 750ps Rise, 35 mil planes,1uF @ 1200mils 750ps Rise, 35 mil planes,1uF @ 1600mils -1000 -1200 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (ns) October 2007 Dr. Bruce Archambeault 65
Time Domain Noise Voltage Across Simulated IC Power/GND Pin (1 amp) Single Capacitor with Various Capacitor Connection Inductance 0.6 0.5 0.4 0.3 750ps Rise, 10 mil planes, 1uF @ 400mils 750ps Rise, 10 mil planes, (2nH) 1uF @ 400mils 0.2 750ps Rise, 10 mil planes, (1nH) 1uF @ 400mils Level (volts) 0.1 0 -0.1 -0.2 -0.3 -0.4 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Time (ns) October 2007 Dr. Bruce Archambeault 66
Time Domain Noise Voltage Across Simulated IC Power/GND Pin (1 amp) Single Capacitor with Various Capacitor Connection Inductance 2 750ps Rise, 10 mil planes, 1uF @ 400mils 1.5 750ps Rise, 10 mil planes, (2nH) 1uF @ 400mils 750ps Rise, 35 mil planes,1uF @ 400mils 750ps Rise, 35 mil planes,(2nH) 1uF @ 400mils 1 Level (volts) 0.5 0 -0.5 -1 -1.5 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (ns) October 2007 Dr. Bruce Archambeault 67
Maximum Time Domain Noise Voltage Across Simulated IC Power/GND Pin Single Capacitor at Various Distances (Fullwave Simulation) 0.8 0.7 0.6 0.5 Voltage (volts) 0.4 750 ps Rise, 10 mil planes,1uF, 2 nH 0.3 750 ps Rise, 10 mil planes,1uF, 1 nH 750 ps Rise, 10 mil planes,1uF, 0.5 nH 750 ps Rise, 10 mil planes,1uF, No L 0.2 0.1 0 0 200 400 600 800 1000 1200 1400 1600 1800 Distance (mils) October 2007 Dr. Bruce Archambeault 68
Maximum Time Domain Noise Voltage Across Simulated IC Power/GND Pin Single Capacitor at Various Distances (Fullwave Simulation) 0.8 0.7 0.6 0.5 Voltage (volts) 0.4 1 ns Rise, 10 mil planes,1uF, 2 nH 0.3 1 ns Rise, 10 mil planes,1uF, 1 nH 1 ns Rise, 10 mil planes,1uF, 0.5 nH 1 ns Rise, 10 mil planes,1uF, No L 0.2 0.1 0 0 200 400 600 800 1000 1200 1400 1600 1800 Distance (mils) October 2007 Dr. Bruce Archambeault 69
Maximum Time Domain Noise Voltage Across Simulated IC Power/GND Pin Single Capacitor at Various Distances (Fullwave Simulation) 1.8 1.6 1.4 1.2 Voltage (volts) 1 750 ps Rise, 35 mil planes,1uF, 2 nH 750 ps Rise, 35 mil planes,1uF, 1 nH 0.8 750 ps Rise, 35 mil planes,1uF, 0.5 nH 750 ps Rise, 35 mil planes,1uF, No L 0.6 0.4 0.2 0 0 200 400 600 800 1000 1200 1400 1600 1800 Distance (mils) October 2007 Dr. Bruce Archambeault 70
Maximum Time Domain Noise Voltage Across Simulated IC Power/GND Pin Single Capacitor at Various Distances (Fullwave Simulation) 1.6 1.4 1.2 1 Voltage (volts) 1 ns Rise, 35 mil planes,1uF, 2 nH 0.8 1 ns Rise, 35 mil planes,1uF, No L 1 ns Rise, 35 mil planes,1uF, 0.5 nH 1 ns Rise, 35 mil planes,1uF, 1 nH 0.6 0.4 0.2 0 0 200 400 600 800 1000 1200 1400 1600 1800 Distance (mils) October 2007 Dr. Bruce Archambeault 71
Maximum Voltage vs Distance to Capacitor for 1 ns Rise/fall time 0.01 uF Capacitor with 0.5 nH ESL and 30 mOhm ESR 1.4 1.2 Maximum Voltage at source (volts) 35 mil FR4 1 10 mil FR4 2 mil FR4 0.8 1 mil FR4 0.5 mil FR4 0.6 0.4 0.2 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Distance From Capacitor (mils) October 2007 Dr. Bruce Archambeault 72
So Far…… • Frequency domain simulations not optimum for charge delivery decoupling calculations (phase not considered) • Time domain simulations using single pulse of current indicate limited capacitor location effect – Connection inductance of capacitor much higher than inductance between planes – Charge delivered only from the planes October 2007 Dr. Bruce Archambeault 73
Charge Depletion • IC draws charge from planes • Capacitors will re-charge planes – Location does matter! October 2007 Dr. Bruce Archambeault 74
Model for Plane Recharge Investigations ε ε = = 4 4 . . 5 5 r r b = 10 b = 10 b = 10 b = 10 Port2 Port2 Port2 Port2 Port1 Port1 Port1 Port1 (4,5) (4,5) (8,7) (8,7) (4,5) (4,5) (8,7) (8,7) d = 35 mil d = 35 mil d = 35 mil d = 35 mil Cdec Cdec Cdec Cdec Port3 Port3 Port3 Port3 (4.05,5) (4.05,5) (4.05,5) (4.05,5) (4,4.95) (4,4.95) (4,4.95) (4,4.95) Vdc Vdc Vdc Vdc a = 12 a = 12 a = 12 a = 12 Decoupling Capacitor : Decoupling Capacitor : I input I input I input I input C = 1uF C = 1uF ESR = 30mOhm ESR = 30mOhm ESL = 0.5nH ESL = 0.5nH DC voltage used to DC voltage used to DC voltage used to DC voltage used to charge the power charge the power charge the power charge the power plane plane plane plane Port 2 represents IC current draw October 2007 Dr. Bruce Archambeault 75
Charge Between Planes vs.. Charge Drawn by IC Board total charge : C*V = 3.5nF*3.3V = 11nC Pulse charge 5A peak : I*dt/2 = (1ns*5A)/2=2.5nC October 2007 Dr. Bruce Archambeault 76
Triangular pulses (5 Amps Peak) October 2007 Dr. Bruce Archambeault 77
Noise Voltage from Inductive Effect of Current Draw (a) (b) Current pulses too small to see charge depletion effects in this time scale October 2007 Dr. Bruce Archambeault 78
Charge Depletion � Voltage Drop 4 3.5 3 V plane [V] 2.5 L s = 1nH 2 L s = 10 nH L s = 50 nH 1.5 1 0 2 4 6 8 10 Time [ns] October 2007 Dr. Bruce Archambeault 79
Charge Depletion vs. Capacitor Distance October 2007 Dr. Bruce Archambeault 80
Charge Depletion for Capacitor @ 400 mils for Various Connection Inductance October 2007 Dr. Bruce Archambeault 81
Effect of Multiple Capacitors While Keeping Total Capacitance Constant The decap locations are 800mils, 1200mils, 2700mils from the power pin (power-ground pins at IC center) Port1 (8,7) (Ls 50nH) • C=1uF • ESL=0.5nH Decap • ESR=1 Ω 10” 1 inch Ground pin Port2 (4,5) (power pin) ε r =4.5 12” October 2007 Dr. Bruce Archambeault 82
Effect of Multiple Capacitors While Keeping Total Capacitance Constant The decap locations are 800mils, 1200mils, 2700mils from the power pin (power-ground pins at IC center) Port1 (8,7) (Ls 50nH) • C=0.5uF • ESL=0.5nH Decap • ESR=1 Ω 10” 1 inch Ground pin Port2 (4,5) (power pin) ε r =4.5 12” October 2007 Dr. Bruce Archambeault 83
Effect of Multiple Capacitors While Keeping Total Capacitance Constant The decap locations are 800mils, 1200mils, 2700mils from the power pin (power-ground pins at IC center) Port1 (8,7) (Ls 50nH) • C=0.25uF • ESL=0.5nH Decap • ESR=1 Ω 10” 1 inch Ground pin Port2 (4,5) ε r =4.5 (power pin) 12” October 2007 Dr. Bruce Archambeault 84
Constant Capacitance 800 mil Distance October 2007 Dr. Bruce Archambeault 85
Constant Capacitance 800 mil Distance October 2007 Dr. Bruce Archambeault 86
Constant Capacitance 1200 mil Distance October 2007 Dr. Bruce Archambeault 87
Constant Capacitance 1200 mil Distance October 2007 Dr. Bruce Archambeault 88
Constant Capacitance 2700 mil Distance October 2007 Dr. Bruce Archambeault 89
Constant Capacitance 2700 mil Distance October 2007 Dr. Bruce Archambeault 90
Example #1 Low Cap Connection Inductance Cap IC PWR GND PCB October 2007 Dr. Bruce Archambeault 91
Example #2 High Cap Connection Inductance Cap IC PWR GND PCB October 2007 Dr. Bruce Archambeault 92
Example #1 Hi Cap Connection Inductance Cap IC PCB PWR GND October 2007 Dr. Bruce Archambeault 93
Example #1 Lower Cap Connection Inductance IC PCB PWR GND Cap October 2007 Dr. Bruce Archambeault 94
Mutual Inductance Helps Reduce Path Inductance Do’s Don’ts J. L Knighten, B. Archambeault, J. Fan, et. al., “PDN Design Strategies: II. Ceramic SMT Decoupling Capacitors – Does Location Matter?,” IEEE EMC Society Newsletter , Issue No. 207, Winter 2006, pp. 56-67. October 2007 Dr. Bruce Archambeault 95
Effect of Capacitor Value?? • Need enough charge to supply need • Depends on connection inductance Charge = C*V October 2007 Dr. Bruce Archambeault 96
Time Domain Noise Voltage Across Simulated IC Power/GND Pin (1 amp) Single Capacitor (with No L) with Various Capacitor Values 0.6 0.5 750ps Rise, 10 mil planes, (0.0 nH) 1uF @ 400mils 750ps Rise, 10 mil planes,0.01uF @ 400mils 0.4 750ps Rise, 10 mil planes, 100pF @ 400mils 0.3 0.2 Level (volts) 0.1 0 -0.1 -0.2 -0.3 -0.4 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (ns) October 2007 Dr. Bruce Archambeault 97
Time Domain Noise Voltage Across Simulated IC Power/GND Pin (1 amp) Single Capacitor (with 0.5 nH Connection L) with Various Capacitor Values 0.6 0.5 750ps Rise, 10 mil planes, (0.5nH) 1uF @ 400mils 0.4 750ps Rise, 10 mil planes, (0.5nH) 0.01 uF @ 400mils 750ps Rise, 10 mil planes, (0.5nH) 100 pF @ 400mils 0.3 0.2 Level (volts) 0.1 0 -0.1 -0.2 -0.3 -0.4 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (ns) October 2007 Dr. Bruce Archambeault 98
Time Domain Noise Voltage Across Simulated IC Power/GND Pin (1 amp) Single Capacitor (with 1 nH Connection L) with Various Capacitor Values 0.6 0.5 750ps Rise, 10 mil planes, (1nH) 1uF @ 400mils 750ps Rise, 10 mil planes, (1nH) 0.01uF @ 400mils 0.4 750ps Rise, 10 mil planes, (1nH) 1000pF @ 400mils 750ps Rise, 10 mil planes, (1nH) 100pF @ 400mils 0.3 0.2 Level (volts) 0.1 0 -0.1 -0.2 -0.3 -0.4 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (ns) October 2007 Dr. Bruce Archambeault 99
Noise Voltage is INDEPENDENT of Amount of Capacitance! As long as there is ‘enough’ charge Dist=400 mils ESR=30mOhms ESL=0.5nH October 2007 Dr. Bruce Archambeault 100
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