Avoiding right-angle wiring is imperative in PCB layout as it is considered a standard for measuring the quality of wiring. This begs the question, how significant is the impact of right-angle traces on signal transmission? In principle, right-angle traces alter the line width of the transmission line, resulting in impedance discontinuities. Not only right-angle traces but also sharp-angle traces can cause impedance changes.

The impact of right-angle traces on signal transmission can be attributed to three key factors. Firstly, the corner acts as a capacitive load on the transmission line, thus slowing down the rise time. Secondly, the impedance discontinuity leads to signal reflection. Lastly, right-angle tips generate electromagnetic interference (EMI).

The parasitic capacitance introduced by the right angle of the transmission line can be approximated using the empirical formula: C=61W (Er) 1/2/Z0. In this formula, C represents the equivalent capacitance of the corner in pF, W is the trace width in inches, εr denotes the dielectric constant of the medium, and Z0 is the characteristic impedance of the transmission line. As the line width of the right-angle trace increases, the impedance decreases, resulting in the occurrence of signal reflection.

After calculating the equivalent impedance with the increased line width using the impedance calculation formula mentioned in the transmission line chapter, the reflection coefficient can be determined using the empirical formula: ρ=(Zs-Z0)/(Zs+Z0). Generally, the impedance change caused by right-angle wiring ranges from 7% to 20%, with a maximum reflection coefficient of approximately 0.1.