Totem-Pole Output configuration found in ICs

Posted on Feb 7, 2014

A type of output structure used with integrated circuits in which one transistor drives the output high while another transistor connected below it pulls the output low. Many ICs use Totem-Pole Outputs, in fact it`s so common that the output structure isn`t mentioned in the data sheet title. An IC with a Totem-Pole Output is the

Totem-Pole Output configuration found in ICs
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default condition. As opposed to an Open Collector Output which is always indicated in the title of the data sheet. The circuit schematic shown below details the internal structure of a TTL triple input NOR gate with a Totem-Pole Output. The Totem-Pole is formed by transistors Q1 and Q2. The schematic and logic diagram are examples of 3-input NOR gates. The output structure will be some deviation of a Totem-Pole but the actual schematic will change depending upon the Logic Family used. Note that the current paths are different between a high and low pulse. A totem-pole output sources current out to the load and sinks current in. Or an output high is derived from Vcc through Q1, and an output low is derived from Q2 to ground. So a rising pulse sees the impedance path of Q1 while a falling pulse see the impedance path of Q2. Depending on the logic function and the logic family there may be components in one or both paths in addition to the switching transistors Q1 and Q2. The different components and the different impedances of the transistors causes a difference between the rise time and the fall time of the output pulse.

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