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U. Glaeser

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FIGURE 3.4<br />

FIGURE 3.5<br />

IPULL-DOWN,<br />

flows through QD into VREG,<br />

resulting in fast pull-down of the output. As the potential at<br />

OUT approaches the “low” level, the potential at node B approaches the “low” level, causing QD to<br />

gradually turn off again. At the same time, QU turns on gradually. When OUT reaches the “low” level,<br />

VOL,<br />

both QU and QD turn on slightly, and a small steady-state current, ISS(L)<br />

, flows.<br />

In this way, the circuit self-terminates the dynamic pull-down action by sensing the output level. By<br />

comparing the output voltage and the pull-down current waveforms in Fig. 3.3 with those in Fig. 3.2, it<br />

is clear that the LS-APD-ECL circuit consumes less dc current than the AC-APD-ECL circuit and that<br />

the LS-APD-ECL circuit offers larger dynamic pull-down current whose level is self-adjusted in accordance<br />

with loading conditions. Therefore, proper and balanced output waveforms can be observed in<br />

the LS-APD-ECL circuit under a wide range of loading conditions.<br />

© 2002 by CRC Press LLC<br />

Pull-up action of LS-APD-ECL circuit.<br />

Pull-down action of LS-APD-ECL circuit.

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