The 2N2/256-BSCP [was: Homebrew Drum Computer] - test-drb@ccmp.vtda.org

21 Dec 2007

From: dkelvey at hotmail.com

...
   Another negative resistance device is the DIAC. These
are
 really cheap but these are knee type curves instead of
 S type, like the TD and Lambda.
  One would have to rearrange these in a parallel configuration
 for a latch or flop, similar to the neon circuits.
  The TD has the advantage that the stable state is lower
 current, not higher current.
  The disadvantage is that that tends to increate the impedance
 of the storage net making it less stable and more susceptible
 to noise. That is why I recommend the shunt resistor to
 decrease the impedance. 
I did suggest DIACs along with the tunnel diodes as being a period 
device, but I think of them more akin to neon bulbs (i.e. great for 
relaxation oscillators and ring counters perhaps) than TDs.

At the time of their debut, I believe that TDs offered the fastest 
performance of any semiconductor active logic.  DIACs (I'm thinking 
of UJT speeds) would not nearly be as promising, it seems to me.

There are patents employing Gunn diodes in logic, but a pair seems to 
be required.    On the other hand, its relative, the IMPATT diode 
seems not have seen use as the active element in logic circuits.  
IMPATTs date from about 1965, so they're *barely* OT for the rules of 
the project.

Cheers,
Chuck