Electronic – BJT push-pull modification

bjt

I am playing with BJT push-pull circuit from a previous question (there are 3 push-pulls with various speedup tricks for comparison):

enter image description here

I've recently realized, that's it's voltage follower, so it's not supposed to show rise/fall times shorter than ones of input signal.

Is it possible to modify it somehow to have more 'steep' output? I don't expect it to be like Schmidt trigger, just want it to have more than 1 voltage amplification near 0.5*VCC.

Is that possible? Probably some fancy level shifting, diodes…

Updated circuit which gave me somewhat desired results. 150 Ohm resistors on the right are load.

enter image description here

Best Answer

First, these are NOT voltage followers. They are inverters. There is no reason their gain magnitude couldn't be more than 1. In fact, I expect all these circuits already amplify, but since you're putting a digital signal in you don't see the amplification when the input is near 1/2 the supply. That's probably a good thing because leaving the input there would fry the transistors rather quickly.

While the gain magnitude is most certainly above 1, it is not predictable or controlled. There are various ways to get that, like adding emitter resistors with some feedback per stage.

If you want positive gain like a Schmitt trigger, then put two of your inverters together with a little positive feedback around the pair.

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