- 2072 Kartik · 2 marks
Impedance matching and discontinuities
Short answer
Impedance matching makes source, line, and load impedances equal (Z_s = Z_0 = Z_L) to prevent signal reflections. Impedance discontinuities (trace width changes, vias, stubs) cause reflections leading to ringing, overshoot, distortion, false triggering, timing errors, and EMI.
Define impedance matching. What is the impact of impedance discontinuities?
Impedance matching is making the source impedance, the characteristic impedance (Z₀) of the transmission line and the load impedance equal (Z_s = Z₀ = Z_L), so that the signal is fully transferred to the load and no reflection occurs.
Impact of discontinuities: any sudden change in impedance (change in trace width, via, stub, connector, layer change, branch, gap in the ground plane) causes part of the signal to be reflected, with reflection coefficient Γ = (Z_L - Z₀)/(Z_L + Z₀). This results in ringing, overshoot/undershoot, signal distortion, false triggering, increased delay and timing error, higher EMI, and loss of signal power.
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