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 with BJTs
Started by ●August 22, 2018
Reply by ●August 22, 20182018-08-22
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
Reply by ●August 22, 20182018-08-22
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
Reply by ●August 22, 20182018-08-22
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
Reply by ●August 22, 20182018-08-22
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
Reply by ●August 22, 20182018-08-22
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 negativeI 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.
Reply by ●August 22, 20182018-08-22
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
Reply by ●August 22, 20182018-08-22
pcdhobbs@gmail.com wrote:> You can also do it with a single transistor at AC.Out of curiosity: do what? Best regards, Piotr
Reply by ●August 22, 20182018-08-22
>> 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
Reply by ●August 22, 20182018-08-22
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