1. Crosstalk

2. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_2 Course outline Contents Digital Signal Model Non Ideal Behavior of Components High Speed Properties of Digital Gate Ground Planes CrosstalkCrosstalk Power Distribution Terminations Crosstalk between two lines Crosstalk analysis Approximations Capacitive coupling (freq. domain) Frequency response Inductive coupling (freq. domain) Inductive vs capacitive crosstalk Near-end and Far-end Capacitive coupling Example of capacitive coupling Inductive coupling Example of inductive coupling Crosstalk in PCB

3. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_3 Crosstalk between two lines reference conductor receptor wire generator wire receptor wire generator wire reference conductor shield receptor wire generator wire reference conductor

4. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_4 Crosstalk between two lines Two effects: –capacitive coupling –inductive coupling Simplified models for analyzing coupling effects

5. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_5 Crosstalk analysis Given the transmission line characteristics, the objective is to predict the noise voltage Frequency domain: –Magnitude and phase of the receptor phasor voltages for a sinusoidal source V S (t)

6. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_6 Approximations Electrically-short line Weak coupling Crosstalk is a linear combination of two contributes: –mutual inductance  inductive coupling –mutual capacitance  capacitive coupling

7. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_7 V 1 (t) + V N (t) C 2G C 1G C 12 Conductors 1 2 R Capacitive coupling (freq. domain) C 1G and C 2G are often negligible

8. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_8 Capacitive coupling (freq. domain) R small  Coupling is reduced by: –decreasing R –increasing the distance between conductors (C 12 decreases)

9. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_9 Capacitive coupling (freq. domain) R large  Coupling is reduced by: –increasing the distance between conductors (C 12 decreases)

10. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_10 Frequency response Noise voltage V N Frequency,  V 1 (t) + V N (t) C 2G C 12 1 2 R Equivalent circuit Frequency response

11. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_11 Inductive coupling (freq. domain) R1R1 I 1 (t) + Conductors 1 2 R2R2 R M V N (t)

12. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_12 Inductive vs capacitive crosstalk For low impedance loads (high currents, low voltages) we expect inductive contribution to crosstalk to dominate the capacitive one For high impedance loads (low currents, high voltages) capacitive contribution to crosstalk would dominate the inductive one

13. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_13 Near-end and Far-end Inductive effect Capacitive effect 1 2 Near end Far end

14. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_14 Capacitive coupling Electric induction between wire #1 and #2 produces a displacement current to flow between wires This current divides in two parts in circuit #2 End crosstalk voltages are of same sign 1 CMCM v NE v FE iMiM 2

15. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_15 Example of capacitive coupling v1v1 time 1 CMCM v NE v FE iMiM 2 Line delay  negligible time v NE v FE

16. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_16 Inductive coupling Current in wire #1 produces magnetic field Magnetic flux variation induces a voltage in wire #2 End crosstalk voltages are of opposite sign v NE = voltage on near-end load v FE = voltage on far-end load 1 2 i LMLM v NE v FE v IND

17. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_17 Example of inductive coupling 1 2 i LMLM v NE v FE Line delay  negligible time v1v1 v NE v FE

18. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_18 Crosstalk in PCB Rule of thumb –In most cases it’s sufficient to separate the traces –Distance between traces at least six times greater than high on ground plane  crosstalk level is  1% of interfering signal u.l. = unit length (y/h = 10)  crosstalk <1% In general, crosstalk problem is negligible 4 u.l. 6 u.l. 1 u.l. Ground plane

19. @ Copyright 1999 - F. Canavero, R. Fantino 7/6/2017Licensed to HDT - High Design TechnologyCROSS_19 Next topic Power Distribution