Last visit was: Sun Nov 28, 2021 11:34 am
It is currently Sun Nov 28, 2021 11:34 am



 [ 5 posts ] 
 Tiny, superfast gates rival programmable logic 
Author Message
User avatar

Joined: Tue Jan 15, 2013 5:43 am
Posts: 186
Logic gates are traditionally supplied in 14- and 16-pin packages containing several identical gates -- an arrangement which often won't exactly suit your needs. For example, a 74ac00 gives you four NAND gates whether you need that many or not. But that barrier -- and the speed barrier -- collapse when using single-gate devices such as those in the 74LVC1G series (NXP, Texas Instruments). Even the largest of these devices are pretty small. And, with typically one gate per package (the 2G series have two gates), they're far less likely to result in leftover, unneeded gates.

A more important factor is routing. PCB traces can be shorter because each device gets located in the spot it's needed. And, best of all, these chips are FAST. :shock: They have a maximum propagation time around 3 ns. For example, 2.7ns is the maximum for a SN74LVC1G10 3-input NAND driving 15 pF at 5 volts Vdd. (Low voltage operation is somewhat slower.)

The attached TI document pertains to products supplied in a single-gate or dual-gate configuration. 5- and 6-pin packages are common, but 8-pin offerings include 74LVC1G139 (half of a 74_139 decoder) and 74VLC3G04, a triple inverter (half of a 74_04).
Attachment:
How to Select Little Logic scya049a.pdf


I've depicted some of the logic functions below, some of which (such as the 3-input XOR) aren't traditional. Also available but not shown are lots of tri-state and open-drain buffers, FET switches and so on. For a complete listing I suggest you visit your favorite supplier's web site and run a search for parts beginning with 74LVC1G. Even that won't be a complete listing, as families other than 74LVC also feature one-gate logic. Have a look for 2G and 3G, too.
Attachment:
sampling of one-gate functions.png


The images below give an idea of size. The 6-pin SOT-23 package -- the largest of the three available packages -- is a good match for protoboard with .050" hole spacing (left), and can, with the use of two flying leads, even be hacked onto protoboard with .1" hole spacing (right).
Attachment:
SOT-23-6 package on .100 and .050 grid.png


Of course PCB mounting is the most comfortable habitat for these chips, and that's what many of you will choose. But I often use wire-wrap or point-to-point, so I designed some breakout boards to bring these tiny pinouts onto a .1" grid. The artwork for my breakout boards can be found at the end of this post.
Attachment:
IMG_2756CrpTchLores.JPG

The first of the two breakouts below is very general. It's a 20-pin design that can optionally be chopped in half. The artwork has traces for power and bypass capacitors but leaves all the signal pins uncommitted. The only assumption is that pins 2 and 5 on each chip are Gnd and Vcc, and most 74LVC chips seem to match this (although other families may not).

The second breakout is a 14-pin design with a more specific function. Most commonly, it would be used to cascade three gates into a fourth gate, resulting in a nine-input gate with a max prop delay of about 6 ns. Note that the gates needn't be identical (can be a mixture of AND NAND XOR NOR etc). One use for a fast, nine-input gate would be for fine-grained address decoding for memory-mapped I/O.

Less commonly, you might have occasion to replace one or more of the gates with a '1G373 transparent latch or '1G175 flipflop. (These have their outputs on pin 4, just as with the AND NAND OR NOR chips.)

-- Jeff
Attachment:
1G breakout 'a' and 'b'.png


You do not have the required permissions to view the files attached to this post.

_________________
http://LaughtonElectronics.com


Last edited by Dr Jefyll on Fri Oct 22, 2021 5:52 pm, edited 2 times in total.



Mon Feb 01, 2016 3:25 am WWW

Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1644
Here's a thought - glue these chips upside down on a small board with some header pins, then wire up point to point. Then the board can be reprogrammed by rewiring.


Tue Mar 22, 2016 8:27 pm
User avatar

Joined: Tue Jan 15, 2013 5:43 am
Posts: 186
I agree point to point is a useful option. And it makes sense to use the third dimension as you say, bringing the IC pins (or at least some of them) up off the board. But rather than flipping the chip on its back I'd prefer to leave it right side up -- and, rather than using glue for attachment, what I'd suggest is to solder each chips's supply pins (which are centrally placed) to pads or traces on the board. That helps keep the board tidy, since two parallel traces make a nice set of supply rails extending to several IC's, and bypass caps can easily be added. The four corner pins of each IC would be bent upward, and it's those pins that would be done individually, point-to-point.

Of course the other option is to use a breakout board. The ones shown above bring the connections onto a .1" grid, and my intention was that they'd insert in an IC socket -- thence to be attached by wire-wrap or any other method of choice.

cheers
Jeff

_________________
http://LaughtonElectronics.com


Last edited by Dr Jefyll on Tue Mar 22, 2016 9:15 pm, edited 1 time in total.



Tue Mar 22, 2016 9:06 pm WWW

Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1644
Sounds good to me!


Tue Mar 22, 2016 9:10 pm

Joined: Mon Oct 07, 2019 2:41 am
Posts: 271
BigEd wrote:
Sounds good to me!

I was thinking they would be good to interface to say a SD card interface.
And PDP-8 fans out there, the flip/chips can now be reduced in making the classic transistor
PDP-8 1/4 size ...


Thu Oct 10, 2019 10:29 pm
 [ 5 posts ] 

Who is online

Users browsing this forum: CCBot and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group
Designed by ST Software