Page 1 of 2
Resistors in TTL
Posted: Mon Mar 30, 2009 12:07 pm
by Jonah Bron
Hello, world!
Is there a resource out there that explains the use of resistors in transistor-transistor logic? I think it has something to do with the fact that transistors amplify, but I'm not sure. Can't find anything on google. I realize that this forum has nothing to do with this subject, but there seems to be a super-saturation of geniuses here.

Re: Resistors in TTL
Posted: Mon Mar 30, 2009 12:42 pm
by Christopher
Resistors are to drop voltage. Given that TTL circuits have a common base and emitter, you have to control the voltage going into each of the two (or more) transistors. Obviously the base and emitter would have different voltages. That is sort of the point of transistors.
Re: Resistors in TTL
Posted: Mon Mar 30, 2009 1:39 pm
by Jonah Bron
What do you mean by "common base and emitter"? I do know that resistors transform electricity into heat, but how is that implemented into an IC to help? Is it because the transistor amplifies the signal from the collector with the base, so that the emitter gives off an amplified voltage, making it so eventually there is too much voltage for the transistor to handle and it burns out (only in situation where collector is 1, base is 1, and is an NPN type transistor)?
Re: Resistors in TTL
Posted: Mon Mar 30, 2009 4:06 pm
by Christopher
As I recall it is because the input voltage is going to the base of one transistor and the collector of the other. Those can't be the same voltage, hence resistors to step down the voltage as necessary.
Re: Resistors in TTL
Posted: Mon Mar 30, 2009 6:38 pm
by Jonah Bron

I'm just a little bit confused. Going to the base of what one transistor, and the collector of what other transistor? Do you mean one transistor and other transistor as NPN and PNP? What can't be the same?
Thanks a lot for the help

Re: Resistors in TTL
Posted: Mon Mar 30, 2009 10:25 pm
by Christopher
Re: Resistors in TTL
Posted: Mon Mar 30, 2009 10:40 pm
by Benjamin
Here's another one:
http://en.wikipedia.org/wiki/Resistor-transistor_logic
If computers didn't exist I'd probably really be into designing, building and playing with integrated circuits, but programming is cheaper and doesn't involve any physical construction. I studied this years ago... cool stuff.
Re: Resistors in TTL
Posted: Tue Mar 31, 2009 6:06 pm
by Doug G
Resistors are necessary to "see" your amplified waveform. For example, if you have a dead short you won't see any voltage differential if you measure with a voltmeter across each end of the short. If you put your voltmeter across each end of a resistor in the circuit you will see a voltage waveform.
E = IR
Re: Resistors in TTL
Posted: Tue Mar 31, 2009 9:37 pm
by php_east
that is incorrect. in ttl, the transistor is not used as an amplifier at all, it is used as a switch.
resistors are used to limit the current inflow towards the base, for correct biasing current towards the base, which will determine the output flow via collector/emitter, passing through the semiconductor hence the word 'transistor'. a resistor is also used sometimes in the output to limit the outflow. the bias determines the state of the transistor output, wether it is logic high (>2 v) or low (<.67v). that's about what i can recall.
Re: Resistors in TTL
Posted: Wed Apr 01, 2009 10:01 am
by Jonah Bron
astions wrote:...cool stuff.
cha.
The diagram in the wikipedia ttl link showed only the power, (not input or output) being regulated. Why is that?
Hmm. But what if the input is high, then wouldn't the resistor push it's voltage tward low? And if it's low, what happens then? Maybe I'm more confused than I thought I was...
Thanks!
Re: Resistors in TTL
Posted: Wed Apr 01, 2009 8:57 pm
by Doug G
Actually, the transistors in ttl logic do amplify. TTL is an IC technology more than an electronic term and is the basis for many logic IC's, but there are other chip technologies too. DTL preceeded TTL (slightly), there is ECL and others. You may want to research how to build a flip-flop from discreet components, since the principle is the same regardless of the way the flip-flop is implemented inside an IC (which is pretty much magic anyway).
Here's another page google turned up.
http://www.educypedia.be/electronics/di ... ogyttl.htm
Re: Resistors in TTL
Posted: Thu Apr 02, 2009 10:11 am
by Jonah Bron
Thanks for the tip. It's pretty hard to find diagrams with discrete components, instead of logic gates, but I found one. Examining now...
Muchas gracias

Re: Resistors in TTL
Posted: Thu Apr 02, 2009 2:18 pm
by Benjamin
Are you building something or just learning about this?
Re: Resistors in TTL
Posted: Thu Apr 02, 2009 6:57 pm
by Jonah Bron
Yes. I find the subject quite fascinating, and am planning on maybe building a few simple robots, programming them with assembly, and using that experience to assist me in my current goal: building my own computer (saving up now) and writing my own operating system. Research areas mostly covered:
SMT soldering
What soldering iron (Weller WLC100)
What microcontroller (Freescale Flexis, 8-bit)
Where to get motors, etc (minimo.com, mouser.com)
Where to get PCBs/how to make them (BatchPCB.com, Google)
And I have a 2'x2'x5/8" piece of aluminum.
Still have a long way to go. Found all the theoretical components for the computer, too. Gonna build a chassis.
Cheerio

Re: Resistors in TTL
Posted: Thu Apr 02, 2009 7:17 pm
by Benjamin
That's cool. If you make anything take some pics and post them someplace.