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2.5 Reflection of DC voltage in Transmission lines 67 Figure 2.5-49 Charge profile in the voltage wavefront region Let us zoom in to the spot on the top wire just underneath the voltage wavefront (Figure 2.5-49). To the left of the wavefront, the charge carriers appear pressed close together. To the right, they remain at a normal spacing. This subtle difference in carrier density on either side of the wavefront creates a small, local electric field pointing to the right. This field does not extend very far. It exists only underneath the rising edge of the travelling wavefront. The rightward-pointing field underneath the rising edge acts only on the charge carriers within its domain, accelerating them forward. Figure 2.5-50 Charge profile on the bottom wire corresponding to top wire region shown in Figure 2.5-49 On the bottom wire, the charge carriers are shoved in the opposite direction, peeling them away from the uniformly-distributed mass of particles to the right, accelerating them toward the battery. This is shown in Figure 2.5-50. Figure 2.5-51 Voltage wavefront reaches the short circuited end of the line At the time when the voltage wavefront reaches the end of the line (Figure 2.5-51), the top wire has compressed charges all along its length. The bottom wire has a deficit of charges which have been taken by the battery and shoved into the top wire. The charge carriers making up the physical wire that creates the short-circuit (shown in green in Figure 2.5-51) experience two effects: pushing from the top wire and pulling from the bottom. + _ _ + _ + Vs Vs COMPRESSED RELAXED AT REST Electric Field + _ _ + _ + Vs Vs COMPRESSED RELAXED AT REST Electric Field AT REST Conquer Radio Frequency 67 www.cadence.com/go/awr

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