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2.5 Reflection of DC voltage in Transmission lines 63 This process continues as the voltage wave continues to travel down the line charging each capacitor through the preceding inductor (Figure 2.5-41). Figure 2.5-41 The voltage wave continues to travel down the line Now what happens when we reach the end of the line? In the case of a pulse, examined in the previous section (2.5.2.1.1), the current looped around at the short circuit, found its way into the penultimate capacitor, which was uncharged, and charged it a voltage equal to –E/2. The current maintained the same magnitude as the incident one. In this case things are different. The penultimate capacitor has been charged to a voltage equal to E/2 and that charge is still there since the incident stimulus has not been removed. As the voltage reaches the end of the line, the last inductor will have current flowing through it but will not charge the last capacitor (greyed out in Figure 2.5-42) whose terminals are shorted. Figure 2.5-42 The current loops around without charging the last capacitor and doubles in magnitude This current from the last inductor will loop around and start flowing into the penultimate capacitor but in opposite direction to the current that initially charged this capacitor (Figure 2.5-33). This will discharge the capacitor and "free" the carriers trapped inside it. Such carriers will act to increment the current flowing around the loop and, since the energy stored in the inductor and capacitor is the same 17 , the loop current will eventually double as the capacitor is fully discharged. This is shown in Figure 2.5-43. 17 The transmission line has a characteristic impedance √ We can therefore write ⇒ i.e. E E/2 I E/2 E/2 E/2 E E/2 E/2 E/2 E/2 I Conquer Radio Frequency 63 www.cadence.com/go/awr

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