Effects of Signal Return Path Discontinuity (RPD) & SSN

One signal switching without reference plane change power via

LG

P

L

G

P

P

G

One signal switching with reference plane change, Red:signal current Blue:Displacement return current Pink:power/ground voltage fluctuation in the form of EM wave

Multiple signals switching with reference plane change, Red: more signal currents

Pink: stronger power/ground voltage fluctuations in the form of EM wave, more signal waveform distortion and skew

Receiver Waveform under the Influence of Simultaneous Switching Noise (SSN)

(As the Number of Simultaneous Switched Drivers Varies, no decoupling caps used, results from Speed2000)

Ideal Case: Trace in top layer, no RPD

8 Drivers4 Drivers

1 Driver

skewringing

Timing and waveform degradation are THE 2 things in SI study. Pwr/gnd as signal RPD affect both through basic EM phenomena.

Effect of Decoupling Caps on Receiver Voltage with 8 Drivers Switching

Simultaneously (SSN reduction, results from Speed2000)

Ideal case: Trace onTop layer, no RPD

32 caps (0603)plus 4 caps (0805)

No decoupling caps4 caps (0805)

Max Overshoot/Undershoot

No decoupling caps: 772 mV

4 caps: 260 mV36 caps: 49 mV

Ideal case: 39 mV

The Electromagnetic Interactions Take Place Inside Packaging

Structuresc a p a c i to r c a p a c i to rc h ip c h ip

s i g n a l t r a c e s

v i a s

P r i n t e d C i r c u i t B o a r d