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Double inverted signal
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Momchilo:
Hi,
I have a 1Vpp square wave from 0 to 1V from a function generator. I want to increase the peak-to-peak voltage to 0V to 5V and I also need the inverted signal from 0V to 5V. The frequency of the square wave will be varied between 5Hz and 200kHz.
I know there are converter and inverter ICs, who would do the job perfectly.
But I tried to do this with some components which I have at home. The inverter is built by a npn-transistor (BC547) and two resistors. It works just fine, also at 200kHz. I thought the simpliest way would be to invert the inverted signal again to get the original square wave with an increased voltage. The schematic is attached and also the LTspice simulation.
But the double inverted signal isn't useable at frequencies higher than 40kHz, I attached a picture of the scope with the 200kHz double inverted signal and the output of the function generator. You can see that the rise time of transistor Q2 is way too slow. If I lower the value of R2, the rise time will be faster, but the voltage of the inverted signal will decrease (voltage divider). In the LTspice simulation the rise time is better than enough.
Is there a simple solution for my problem? Thanks for your help.
Best regards
Momchilo 
Zero999:
It's more likely the transistor's base charge, which is responsible for the slow off time and rise time of the double inverted signal.

Try removing R2 altogether and adding another transistor to give the inverted output. Another possibility is adding a 100pF capacitor across R2, but that might delay the rise time of the inverted signal too much.
rstofer:
If you remove R2 the inverted output will never rise higher than Vbe of the second inverter.
StillTrying:
 :-/O 'ed
David Hess:
A single diode Baker clamp needs the lower forward voltage drop of a schottky or germanium diode to work.  A silicon diode Baker clamp can be made with two diodes.

https://en.wikipedia.org/wiki/Baker_clamp

Instead of a Baker clamp, I would start by bypassing R2 with enough capacitance to allow fast removal of base charge like Hero999 suggests.  100 picofarads is about right but try different values.

I am not familiar with the switching characteristics of the BC547 but that storage time seems awfully long.  I would expect more like 200ns maximum.

The circuit you really want is called a "data slicer" and is commonly made with a comparator, resistor, and capacitor but a couple of transistor inverters like you have should work also.

https://www.maximintegrated.com/en/app-notes/index.mvp/id/3435
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