Hello Everyone,

I believe that for the most part I know how the TTL works, but I still have a couple of doubts that I would love if someone could clarify!

Most of the configurations that I see all have the following resistors:

But I have yet to read why do they select those specifics resistors, does anyone knows why those specific values are chosen?!

I believe I know how to do it but... How would you compare the delay times between the input and the output?


Thanks in advance!

 

The resistors are there probably to make sure the inverter can switch quickly without being overdriven. I can't say much about that particular configuration, but I assume it was a choice to get either better speed, noise immunity or to meet some input requirements.

To calculate the delay I imagined you'd have to have some model for the transistors which would include junction capacitances, gains, Vbe, Vce_sat and some assumption of input drive and output load. If you've got a way to estimate that, it's probably more than I know. I would think the best way to figure it out is empirically or by trusting the datasheet waveforms/specs.

 

I figured that I had something to do with how to saturate the transistors and because of that the switching speeds but I wanted to make sure that I was not missing something...


Thanks for the reply!