6.Transmission Line Effects in High Speed Digital PCBs 射频

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Transmission Line Effects in High Speed Digital PCBs中華大學 通訊系 田慶誠 tien@chu.edu.tw 03 5186030

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Introduction of Waves

Vp: Phase velocity

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Lumped v.s. Distributed Circuit Lumped Circuits

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Lumped v.s. Distributed Circuit Definitions of lumped element (1) Input current amplitude = Output current amplitude (2) Input current phase = Output current phase

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Lumped v.s. Distributed Circuit Distributed Circuit

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Lumped v.s. Distributed Circuit What “Distributed” means

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Rise Time v.s. Travel Time Tr: Rise Time Td: Delay Time

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Digital Interconnection Rules 數位工程師的 Rule of thumb Signal path can be treated as:

A lumped element, if Tr > 6 Td (Short ckt, series resistor, shunt capacitor)

A lumped model, if 2.5 < Tr/Td < 6 (Series inductor with shunt capacitor)

A distributed model, if Tr < 2.5 Td (Transmission Line or multi-section LC model)

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Why Tr > 6 Td ? Example: Rs = 0.25 Zo, RL=

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Why Tr > 6 Td ? Multi-reflections occurred at load Tr = 2 Td Tr = 4 Td

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Why Tr > 6 Td ? Strong ringing Tr = 2 Td Smooth ripple Tr = 4 Td

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Example of High-Speed IC Interconnection CMOS On-chip 1mm interconnection Vp= 0.5c = 150mm/ns Td=1mm/Vp = 0.067ns Rule of Thumb only worked as: Tr > 6Td= 0.04ns -1 = 3GHz FCLK < (8Tr) Inductance extraction now is very important !!中華大學 通訊系 12

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Example of High-Speed IC Interconnection10mm interconnection between IC’s Vp= 0.6c =180mm/ns Td= 10mm/Vp = 0.056ns Rule of Thumb only worked as: Tr > 6Td= 0.33ns -1 = 375 MHz FCLK < (8Tr) Distributed analysis now is very important !! 中華大學 通訊系 13

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Sinusoidal EM Wave Oscillations in Time

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Sinusoidal EM Wave Wave Motion in Space

中華大學 通訊系

Transmission Line Effects in High Speed Digital PCBs 射频电路基础(台湾)经典

Period v.s. Travel Time Period T = 1/freq Td= L/(freq* ) VBB’(t) is different from VAA’(t)

中華大學 通訊系