Negative resistance with BJTs

a four layer diode, consisting of alternate p, n layers acts as a
negative resistance, and can be realized in practice with a pair
of NPN and PNP transistors, connected in specific ways. Now, is
it possible to achive this a series connection of two discrete 
diodes ? I was just thinking about it. 

dakupoto wrote
>a four layer diode, consisting of alternate p, n layers acts as a
>negative resistance, and can be realized in practice with a pair
>of NPN and PNP transistors, connected in specific ways. Now, is
>it possible to achive this a series connection of two discrete 
>diodes ? I was just thinking about it. 

Negative resistance can be done with only one diode,
it is called a tunnel-diode or Esaki_diode:
 https://en.wikipedia.org/wiki/Tunnel_diode

Just bias the diode at the right current where I versus V is negative

You can do it with one or more tunnel diodes, but not with ordinary ones because they have no gain. 

You can also do it with a single transistor at AC. 

Cheers

Phil Hobbs

On Wednesday, 22 August 2018 12:43:24 UTC+1, daku...@gmail.com  wrote:

> a four layer diode, consisting of alternate p, n layers acts as a
> negative resistance, and can be realized in practice with a pair
> of NPN and PNP transistors, connected in specific ways. Now, is
> it possible to achive this a series connection of two discrete 
> diodes ? I was just thinking about it.

Maybe if you sawed them open at exactly the right point & fused the silicon dies together... otherwise they're just 2 diodes, with the middle p&n layers not in contact with each other.


NT

On Wed, 22 Aug 2018 04:43:18 -0700 (PDT), dakupoto@gmail.com wrote:

>a four layer diode, consisting of alternate p, n layers acts as a
>negative resistance, and can be realized in practice with a pair
>of NPN and PNP transistors, connected in specific ways. Now, is
>it possible to achive this a series connection of two discrete 
>diodes ? I was just thinking about it. 

Some diodes have a negative resistance region, but it's obscure. You
can tease a zener diode to oscillate badly. RF diodes, gunn and such,
oscillate. I think an avalanche photodiode will oscillate in the right
circuit.

An LED and a photodiode in series? In other words, an optocoupler with
CTR > 1.

As a kid, I tried using two diodes as a transistor. Apparently lots of
people did that.


-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

In article <pljjaf$1c1o$1@gioia.aioe.org>, 698839253X6D445TD@nospam.org 
says...
> 
> Negative resistance can be done with only one diode,
> it is called a tunnel-diode or Esaki_diode:
>  https://en.wikipedia.org/wiki/Tunnel_diode
> 
> Just bias the diode at the right current where I versus V is negative

I think I've still got a commercial one somewhere, left over from my 
research in the 1960s. With the right bias they would oscillate at very 
high frequencies (for those days!)...

Mike.

John Larkin wrote:

> RF diodes, gunn and such, oscillate.

Gunn is not even a diode, or -- if you prefer -- a junctionless one. :-]
Amazing construction, BTW.

 > As a kid, I tried using two diodes as a transistor. Apparently lots of
 > people did that.

+1

When you grow up, you start using transistors as diodes...

	Best regards, Piotr

pcdhobbs@gmail.com wrote:

> You can also do it with a single transistor at AC.

Out of curiosity: do what?

	Best regards, Piotr

>> You can also do it with a single transistor at AC. 

>Out of curiosity: do what? 

Make a negative resistor. Start with an emitter follower and put a small capacitance on the emitter. The input resistance goes negative. That's why you have to use beads, anti-snivet resistors, and so on. 

Cheers

Phil Hobbs

On 22/08/2018 12:43, dakupoto@gmail.com wrote:
> a four layer diode, consisting of alternate p, n layers acts as a
> negative resistance, and can be realized in practice with a pair
> of NPN and PNP transistors, connected in specific ways. Now, is
> it possible to achive this a series connection of two discrete
> diodes ? I was just thinking about it.
> 

You used to be able to buy four-layer diodes (also sometimes called 
Schockley diodes - not to be confused with Schottky!) in a range of 
voltages. Became obsolete mid 1970s. I had to service gear that used them.

If you accept fudging the rectifier part of the name of an SCR into what 
you'd call a diode then that is a four-layer diode. Leave the gate 
terminal open and at a high enough voltage it will exhibit negative 
resistance !!

piglet