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ttl or gate


telecombug
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hi everybody
i have a project over TTL OR gate. and i wanna know about its circutry specially which transisters should i use and how much resistances should be used.........my last date of submission iz 24th april.....
..............please help me over this project!!!!!!!!!!!!!!

telecombug

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The problem with a simple gate is the slew rate. The gain is not high enough through the transition. A low to high transition will not produce a high quick enough. If you make the gain very low with a pulse input, you get a pulse output the with the same reduction that you would have with a sine wave. A reduced amplitude means a lower rate of change.

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  • 2 weeks later...

Hotwaterwizard,
Your very nice circuit actually is RTL, not TTL. I hope that Telecombug doesn't lose marks for that oversight.

Kevin,
Do you see how this OR gate works? It is simply that one transistor OR the other transistor OR both transistors turn-on the LED.
There is no phase-splitter.

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  • 2 weeks later...

A phase splitter is what allows you to get high gain from the totem pole ouput. The totem pole is two NPNs. It is interesting that one NPN is setup for amplification while the other is setup as a voltage follower. I think this is because the phase splitter produces enough gain for the voltage follower. So the overall high gain is obtained from the splitter producing the high gain for the voltage follower and the totem pole ouput producing high gain. There is no doubt that the configuration was designed for handling the large signal, while providing the high gain slew for the transition.

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Kevin,
An emitter follower has a voltage gain of 0.99 or more. It does not have a transition and its output goes from low to high just as fast as its input because its output follows its input.

Any very high-speed circuit doesn't have much gain, and any very high-gain circuit doesn't have much speed.

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