Address Collisions When Four Parts Share One I2C Bus
Resolve four-part I2C address collisions using 4-state pin strapping, quad-channel switches, or address translation ICs based on BOM cost and driver complexity.
Star Routing Stub
Trace Geometry
Printed circuit board layout structures branch high-frequency transmission lines from a single central junction point to multiple destination receivers through short conductive trace stubs. A star routing stub creates an impedance discontinuity along high-speed signal paths, causing energy reflections and degradation of signal edge transitions. The routing topology becomes problematic when trace stub lengths exceed one-tenth of the signal rise time electrical length.
Signal Reflection
Unterminated trace branches act as open transmission line stubs that reflect high-frequency energy back toward the driving source. These reflections create ringing, overshoot and undershoot on signal waveforms, degrading receiver logic noise margins.
Radiation Level
Impedance mismatches created by branching trace stubs convert differential mode signals into common mode noise components. Radiation from unbalanced star branches increases electromagnetic interference emissions, causing failure in agency compliance testing. When high-speed clock or data lines utilize star routing stub patterns, timing jitter increases significantly across downstream receiver inputs.
Layout engineers mitigate reflection issues by inserting series termination resistors at each branching node or utilizing point-to-point daisy chaining. Signal integrity simulations model stub transmission line behavior before finalized board layout fabrication.
Layout Verification
Time-domain reflectometry measurements quantify trace impedance variations caused by physical branching points on printed circuit boards. High-speed design rule checks flag unterminated stub lengths exceeding critical timing thresholds during layout design.