Monday, November 24, 2014

Breaking the speed limits of classic TTL based homebrew RF designs*

Breaking the speed limits of classic TTL based homebrew RF designs*
*with Potato Chips!

Hello. This post shares an idea about using highspeed TTL chips in classic TTL circuits.

When I first heard about Potato Semi AKA Potato Chip, a semiconductor company, I thought that maybe it was just a joke. If you read some of the wording on their webpage, there are a lot of "potato chip" jokes & puns, playing on their brand name, hidden throughout the text. However, once I saw that not only was this a real company but that they are offering high speed (1GHz+) versions of classic TTL chips, I immediately got excited. There has been a great number of TTL based homebrew projects published over the years. These circuits have often been restricted to a few bands due to the maximum frequency limits of the TTL families used in these projects. With the new availability of these highspeed chips, perhaps we can "break the speed limit" of these old projects and expand them out into new bands, higher up into VHF or even UHF. Certainly there are many other design considerations that will come in to play when building for higher frequency VHF/UHF circuits. But perhaps it would be worth starting by experimenting with low VHF frequencies just above the frequency limits of previous designs.

Potato Semi currently has 24 highspeed TTL chips listed. They call these chips their 'G Series GHz TTL/CMOS logic ICs'. Thats a good starting point for determining which classic TTL homebrew design may be viable for "scaling up". The chips are surface mount but I have a good quantity of SMD breakout boards. If you decide you would like to experiment with these chips for homebrew but have difficulty working with SMD components. Send an email & I will work out a way to post you a couple SMD breakout boards for the package type you will be working with. In exchange, it would be most appreciated if you could share the results of your experimentation (even if just a sentence about a catastrophic failure).

This is just an idea. For all I know, there will be some significant issue with using these chips for homebrew RF design at frequencies higher than the classic TTL families where capable of. But I wanted to at least get the idea out there to others that have a drive to experiment too.

Is there a serious flaw in this idea that I haven't thought of yet? It will certainly require experimentation. I need to be able to acquire a few chips first, that cost money so that will take a little time to happen. Maybe you have already tried this. If so please share your thoughts, success, failures. Maybe you know that this is doomed from the start, if so, please speak up so we can discuss this. I am just passionate amateur homebrewer so there is a great deal that I do not know and will never understand but I love to learn, so please feel welcome to share your wisdom.

The following is from their website, potatosemi.com (underline & bold added by me - also "low cost" = $3.00 per chip via their ebay store)

"GHz CMOS Output
CMOS technology has been widely used for more than 50 years. It delivers low cost with high yield; however due to the unbalanced CMOS structure, it will generate high noise into power and ground. In the past 50 years of IC history our GHz CMOS output driver is the only technology that will reduce your chip internal ground and power noise without sacrificing your output performance. Our low noise technology allows the output frequency to be 7 to 10 times faster than anyone else in the world. In addition, this low noise technology allows any ICs with our output drivers to deliver accuracy without errors. The example below shows the output signal from our standard logic 74G32. The VCC is 3V. The output frequency from the measurement is 2 GHz with probe load. The maximum frequency will be more than 2 GHz. VPP is 2.075V, Vhigh is 2.175V and Vlow is 100 mV."

This is pretty exciting for me, as I haven't worked with TTL/CMOS that are capable of such high speed. I can't wait to start experimenting! Just gotta save up my pennies to get some of these yummy potato chips. Please note that I am in no way associated with Potato Semi. I'm just a curious homebrewer.

73, stay fluxy & keep your iron hot!
-KE0BFF