Thanks for great clip. Tunnel diodes are quantum mechanical devices. The electrons tunnels through the barrier as the barrier become too thin, instead of going over it. Just like science fiction movies, that people and things go through wall. The tunneling speed is much faster than speed of light, and is almost infinity. So, it is fun to investigate it. To get a clean oscillation, you need to measure the negative R of tunnel diode and cancel it with almost the same amount of positive resistance. So, putting a low resistance pot and adjusting it to get a clean oscillation. Of course, I would put diode and tank and the pot all in parallel, instead of series as you have it here. Also, it might be a good idea to have a DC block capacitance between tunnel diode and the pot and tank. As you know, to get a microwave oscillation, you replace your C & L of the tank with pieces transmission line that intersect your main transmission line in a point like a bow tie or use some sort of resonant cavity. Also Tunnel diodes are very expensive and people use NPN transistors ( like 2n2222) backward ( ie. emitter to positive and collector to negative ) to get the similar effect. In this configuration as the depletion region in the base increases as a result of emitter to base biasing the base region gets smaller and smaller until the carriers can tunnel through the barriers. The reason for backward use of NPN transistors is that emitter region is doped much higher than the base region and therefore by backward biasing it almost all of the depletion region will extend in the base region and decrease the effective base thickness. Other negative resistance devices, such as IMPATT and GUNN Diodes, are fun to play with.
thanks dude! Really well taught. As a low frequency power guy, I think these RF diodes are crazy interesting. I was thinking of ways to treat the diode as a variable attenuator. If you push more DC bias through the diode, does the RF insertion loss decrease?
When I started with electronics, I said to myself that I would never work with RF. You, Sir have changed my mind with all your excellent videos. I keep going back to watch videos for ideas. Thanks a bunch!
Google or duck duck go can be your friend: tunnel diode amplifier, tunnel diode oscillator. I have one somewhere, and this makes me want to dig it out and experiment a bit with it. Thanks.
The tunnel diode speed is indeed practically limited onl by the circuit parasitics, but the speed of regular (I mean NPN or so; you still need a hf type) modern transistors is so the real life limitation is also just in the parasitics, so bottom line about the same. That means you can make a negative resistance using a pair of such high frequency transistors (and their bias source) and you end up with very similar performance. On top of that, unlike the real tunnel diode, the key parameters of the transistor pair based negative resistance (mainly the slope and the peak/valley flip currents) are extremely well predictable and controllable (you just need to know the bias current and the temperature, literally nothing else), so consequently these become way more predictable and stable in a real circuit. That is the reason why tunnel diodes are a thing of the past for vast majority of the applications. And because transistors are easy to integrate, the transistor pair negative resistance is a structure is used practically everywhere in modern radio and many analog circuits (oscillators, Q-boosters for on chip LC resonator tanks, synchronous clocked comparators in AD converters, gain boosters in low power opamps and comparators,...)
I have worked in RF engineering over 50 years designing varactor tuned rf front ends for television receivers. We heard about tunnel diodes in the 60s, but no one ever came up up with a good, cost-effective use for them.
Great tutorial Alan, and my favorite "lost art" subject, too. Thanks! Maybe worth noting that these magical things are no longer made, so parts like your test subject are rare and possibly quite expensive. These days the best way to experiment is to source old-stock Russian tunnel diodes on eBay.
Well, a company named American Microsemiconductor seems to be in the business of making tunnel diodes, although they are a bit pricey ... but if one TD gets a piece of test equipment operational again, one hundred US$ might be worth it!
Thanks for a great trip down memory lane, Alan! As a budding ham and EE back in the late 60's, Dr. Esaki's little wunderkind fascinated me. Actually built several gizmos around the GE 1N2939....a 100 kHz. crystal calibrator, 2 M foxhunt transmitter, and a Heathkit Tunnel Dip Oscillator (which still sits on my shop shelf, working to this day!).Often thought what a great electronic countermeasures device a tunnel diode would be, with it's harmonic-rich output coupled to a broadband, high power GaNi amplifier. ;>)
Great video! Funny thing is, there is a question about tunnel diodes in the current "extra" exam question pool. Never really given them much thought due to their applications. I never really given them much thought. You did an excellent job showing just how they react.
Hello Alan. Years ago I came across Unijunction transistor which had also a negative region in its characteristic like the tunnel diode. Can you explain what is the function of the third "foot" and what circuits was it used for?
Superb as usual. I could be useful if you write on the notes used during the video the episode number so as to have a quick reference between the document and the video. Maybe in the filename or maybe just handwritten on the papers. Thanks as usual. CH!
Well, that's totally unexpected! After only little more than five years, the links to the tekwiki documentation are all dead. Have they been transferred somewhere else or are they gone for good?
Outstanding Alan! Especially the links. (I have 500 and 400 series Tek scopes!) I had thought of suggesting this topic, then thought -"nah, too niche" -LOL!
WHY don't presenters (this includes textbooks) 'shade out' that negative resistance region!!?? You will never see that 'region' on a curve tracer nor will you see it* using using slowly stepped manual meters and potentiometers ... I think it does a disservice to 'gloss over' this aspect of Tunnel Diode behavior. * Outside of the device oscillating, giving the impression it is in that region, as you demonstrated.
Finally an explanation of Tunnel Diodes in actual (good) English that is understandable. Yours should be the first option to come out when doing a search for Tunnel Diodes on youtube. Unfortunately it is not.
Page 330 diode (Electronics) = (1) Simplest electron tube, with a cathode and anode; used because of undirectional and hence rectification properties. (2) Semiconductor device with similar properties, evolved from primitive crystal rectifiers for radio reception.
Hi Alan, I just found out about something called a "Shockley Diode". It has a similar IV curve to the tunnel diode. Perhaps it would make a good subject for a future video?
@w2aew I was remembering this video while exploring the "Esaki Effect" to make the @boldport club project #2 blink ( ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-PPUZth8RfCE.html). Thanks for continuing to produce great content - I always looks out for the next "circuit basics"!
Looks similar to a crystal, like the 455 khz one in my Hallicrafters...in the alignment you adjust the coil to the dip in the crystal...or the center of the crystal..
My electronics teacher in 8th grade showed us a circuit made from a few transistors which behaved like a tunnel diode. Does anyone have such a diagram?
Hello Allen great video. I have seen in many Tektronix scopes that 2 tunnel diodes were used as Triger switch. Can you (will you) explain in a video who they did the work. (pre firing, firing, biasing as triggers are set to differend levels)?
I used to wonder why they don't use tunnel diodes in microwave applications. But I guess they don't really operate at a very high power, especially compared to a cavity magnetron, do they? This channel's great. It's been getting me more into RF stuff. Thanks for taking the time and effort to make these. Cheers.
The two diodes set up a fixed voltage on the base of the transistor, which puts a fixed voltage across the 100ohm emitter resistor. A fixed voltage across a resistor results in a fixed current. Since the emitter current and collector current are virtually the same, the collector becomes a source of a fixed current - thus a current source. Check out my video on current sources: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-xR0RfmmRhDw.html
I don't recall, but will say that the oscillation frequency will be highly dependent upon the parasitic inductance and capacitance of the connected equipment.
Great video. I'm fascinated by negative resistance devices. It'd be great if you could cover lambda diodes. I found out about them recently and ordered some P channel JFETs so I could play with them.
It is just to setup a bias voltage on the base of the transistor that is a fixed ~1.4V below the 12V rail, which puts a fixed ~0.7V across the emitter resistor, which in turn makes the transistor source a constant current.
Another excellent tutorial. I especially appreciate seeing how you use simple instrumentation to perform basic device characterization (I.e., tracing the I vs. V curve). Thanks very much for making and sharing this tutorial.
Many circuits become unstable with a negative resistance. Normally, when the the voltage across a decreases, the current drawn also decreases. This device has a negative resistance region - when the voltage decreases the current increases and vice versa. This leads to instability in many circuits.
TheHue's SciTech They are difficult to find these days. However you can often find surplus or new old stock on Ebay. There are a few specialty semiconductor houses that will still make them, but they won't be cheap! njsemi.com/parts/?search=1n2927 download.njsemi.com/1N2927,A%20-%201N2934,A.pdf www.advancedsemiconductor.com/pdf/1n2927.pdf
I really enjoy your video's, they are very informative. But what hardware (sockets) do you use to plug components into? I would like to get some for when I am experimenting. Thanks again and keep up the wonderful video's. 73's WK4DX
Fred Henderson They are pin sockets made by Mill Max. I bought them through Mouser. They have dozens of sizes and styles, so you'll have to decide which work best for you. Here's the Mouser catalog pages: www.mouser.com/catalog/catalogusd/647/1848.pdf www.mouser.com/catalog/catalogusd/647/1849.pdf
An LC parallel tank circuit at resonance does indeed have a high impedance. This video explains the details: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-hqhV50852jA.html
I have not encountered one of them yet, AFAIK, but I’m ok with that. Since I didn’t know they existed, if I didn’t have a schematic, I would have questioned the validity of the diode, but your explanation gave a new outlook in case I came across one of those.
Great, I think that with your talent some video for total begginers would be nice too. You know just some fast sum-up of A,V,R,L,C and diodes. I wanted some video which would give some basic idea and motivation to study it more for few friends which knows only ohm's law but i found nothing.
