Design Con 2015
Breaking News
Comments
Newest First | Oldest First | Threaded View
<<   <   Page 3 / 3
Duane Benson
User Rank
Blogger
Re: Unequal output source/sink
Duane Benson   6/26/2014 11:38:32 AM
NO RATINGS
re: "FINALLY an explanation of why active-low switches and LEDs were preferred."

That's quite interesting. I hadn't heard the explanation before. I missed the double emitter explanation too - although, I can certainly envision how it would work.

FlyByPC
User Rank
Rookie
Re: Unequal output source/sink
FlyByPC   6/26/2014 10:15:47 AM
NO RATINGS
Wow -- FINALLY an explanation of why active-low switches and LEDs were preferred. That makes perfect sense, now. Thank you, sir!

Kinnar
User Rank
CEO
Re: Unequal output source/sink
Kinnar   6/26/2014 12:50:31 AM
NO RATINGS
Developments never make fundamentals old, these things are still being taught the way they are in the curriculum in many countries. And it really helps to explain and test the small circuits, as a stepping measure to bring the students at the current technology usages. 

Wnderer
User Rank
CEO
The Soul of A New Machine
Wnderer   6/25/2014 4:19:42 PM
NO RATINGS
The picture of the Data General/Nova board reminds me of a great book about engineering. Tracy Kidder's ' The Soul of a New Machine'

http://en.wikipedia.org/wiki/The_Soul_of_a_New_Machine

betajet
User Rank
CEO
Unequal output source/sink
betajet   6/25/2014 4:06:39 PM
While the pull-up transistor in the TTL totem-pole output stage is stronger than RTL's resistive pull-up, the pull-down transistor is typically 40 times stronger that the pull-up.  IIRC, a standard TTL output can sink 16 mA but source only 0.4 mA.  That's OK if you're driving other TTL gates, since TTL inputs have the same 40:1 asymmetry.

The asymmetry meant that TTL-based designs almost always used active-low drive for LEDs and active-low push-buttons.  Nowadays CMOS outputs are generally symmetric, but old-timers like me still prefer active-low if an output needs a lot of current.

betajet
User Rank
CEO
Multiple-Emitter Transistors
betajet   6/25/2014 3:43:59 PM
Nice 'blog, but I have a quibble about the LSTTL circuit diagram.  According to Wikipedia, LSTTL didn't show up until 1976 so you're a few years early.

Here's Wikipedia's diagram of a proper 1964 TTL circuit with that wonderful multiple-emitter transistor input stage that's so much fun to explain to undergraduates:



 

<<   <   Page 3 / 3


Top Comments of the Week
Flash Poll
Like Us on Facebook

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Life
Frankenstein's Fix, Teardowns, Sideshows, Design Contests, Reader Content & More
Carlos Bueno

Adventures in Userland
Carlos Bueno
Post a comment
Editor’s Note: Excerpted from Lauren Ipsum: A story about computer science and other improbable things, author Carlos Bueno introduces us to Lauren and her adventures in ...

Max Maxfield

Tired Old iPad 2 vs. Shiny New iPad Air 2
Max Maxfield
8 comments
I remember when the first iPad came out deep in the mists of time we used to call 2010. Actually, that's only four years ago, but it seems like a lifetime away -- I mean; can you remember ...

Martin Rowe

Make This Engineering Museum a Reality
Martin Rowe
Post a comment
Vincent Valentine is a man on a mission. He wants to make the first house to ever have a telephone into a telephone museum. Without help, it may not happen.

Rich Quinnell

Making the Grade in Industrial Design
Rich Quinnell
16 comments
As every developer knows, there are the paper specifications for a product design, and then there are the real requirements. The paper specs are dry, bland, and rigidly numeric, making ...

Special Video Section
The LT8640 is a 42V, 5A synchronous step-down regulator ...
The LTC2000 high-speed DAC has low noise and excellent ...
How do you protect the load and ensure output continues to ...
General-purpose DACs have applications in instrumentation, ...
Linear Technology demonstrates its latest measurement ...
10:29
Demos from Maxim Integrated at Electronica 2014 show ...
Bosch CEO Stefan Finkbeiner shows off latest combo and ...
STMicroelectronics demoed this simple gesture control ...
Keysight shows you what signals lurk in real-time at 510MHz ...
TE Connectivity's clear-plastic, full-size model car shows ...
Why culture makes Linear Tech a winner.
Recently formed Architects of Modern Power consortium ...
Specially modified Corvette C7 Stingray responds to ex Indy ...
Avago’s ACPL-K30T is the first solid-state driver qualified ...
NXP launches its line of multi-gate, multifunction, ...
Doug Bailey, VP of marketing at Power Integrations, gives a ...
See how to ease software bring-up with DesignWare IP ...
DesignWare IP Prototyping Kits enable fast software ...
This video explores the LT3086, a new member of our LDO+ ...
In today’s modern electronic systems, the need for power ...