Low voltage negative resistance oscillator design, lessons learned

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Don't bother with discretes if you want a negative resistor when you  
have low psu headroom, all the discrete negative resistance topologies,  
lambda diodes, foldback limiters, etc. are bad at a couple volts and are  
seriously fussy with respect to how you load them and have lousy tempcos  
down there.

get an AD8515 for 45 cents and save yourself the trouble

Re: Low voltage negative resistance oscillator design, lessons learned
On 8/8/19 3:24 AM, bitrex wrote:
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You can build an okay oscillator using piglet/Win Hill's topology from  
the AoE x-chapters, I got an LC working down to about 1.8 volts with  
that one with a fairly low Q coil using the negative R to cancel it. a  
wide tuning range is impossible though because the slope of the negative  
resistance changes with load and there's not enough headroom to easily  
buffer it to isolate it from the tank, there's almost always too much  
gain or too little and...bla bla bla world of pain, larry.

Re: Low voltage negative resistance oscillator design, lessons learned
On a sunny day (Thu, 8 Aug 2019 03:24:11 -0400) it happened bitrex

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You did not try a tunnel diode?

Re: Low voltage negative resistance oscillator design, lessons learned
On 8/8/19 4:29 AM, Jan Panteltje wrote:
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I don't think I've ever even _seen_ a tunnel diode in the real world,  
much less used one for anything! aren't they usually used for microwave  
frequency oscillators and such? I'm not going that fast.

Re: Low voltage negative resistance oscillator design, lessons learned
On a sunny day (Thu, 8 Aug 2019 12:52:35 -0400) it happened bitrex

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Few MHz works OK too, were used in the FM modulator of some Ampex quadruplex video recorders,
say 5 MHz to 7 MHz sweep or there about.

ebay has plenty:
 https://www.ebay.com/itm/254034572875

AFAIK the frequency low side does not have a limit.
  https://en.wikipedia.org/wiki/Tunnel_diode

Not sure that will work in your circuit,  
what exactly are you trying to accomplish with that circuit?

Re: Low voltage negative resistance oscillator design, lessons learned
On 8/8/19 1:14 PM, Jan Panteltje wrote:
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Increasing the Q factor of a pathologically low-Q coil, like a Q of say  
2 at 3 MHz, so you can build a tank-type oscillator from it at a lower  
frequency than up where the L has a good Q which might be 50 or 100MHz.  
at low voltage, say 2 volts.

A cheap AD8515 works down to 1.8 volts and with 3 resistors in the  
negative-resistance configuration, even at 2 v it has enough oomph and  
bandwidth to make even a crap L ring nicely in a tank circuit like:

<https://imgur.com/a/WZqskyw



Re: Low voltage negative resistance oscillator design, lessons learned
On a sunny day (Thu, 8 Aug 2019 14:26:44 -0400) it happened bitrex

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OK, got the idea.
If you look at the wikiedia link I gave, enlarge the picture of the Tek trace
  
https://en.wikipedia.org/wiki/Tunnel_diode#/media/File:I-V_curve_of_10mA_germanium_tunnel_diode..jpg

then you see the middle of the negative resistance area is around 325 mV for
a Ge tunnel diode, ebay has those too it seems:
 https://www.ebay.com/itm/202519120776

But if your solution works for you OK.



Re: Low voltage negative resistance oscillator design, lessons learned
On 8/8/19 2:26 PM, bitrex wrote:
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Unfortunately negative resistors don't have imaginary noise. ;)

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Low voltage negative resistance oscillator design, lessons learned
On 8/8/19 3:59 PM, Phil Hobbs wrote:
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well clearly you just need to couple them to a "negative heater" and  
cool them down!


Re: Low voltage negative resistance oscillator design, lessons learned
On 8/8/19 4:39 PM, bitrex wrote:
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Sorry, I mean un-heat them.

Re: Low voltage negative resistance oscillator design, lessons learned
On a sunny day (Thu, 8 Aug 2019 16:39:41 -0400) it happened bitrex

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I stil wonder, from the room temperature super conductor postings recently
if one can use ultrasound to slow the motion of atoms in a crystal down
like we use laser cooling to do it with a gas.
I want a Usenet patent for that,

I should try it and measure it but am no physicists, limited lab space and equipment, lame excuse I know.

so then a resistor element with piezo cooler... noise reduction, probably gives you the piezo signal
hey, maybe we can filter that out, oh wait
LOL



Re: Low voltage negative resistance oscillator design, lessons learned
Jan Panteltje wrote:

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I wonder if there is a loose analogy between the evanescent component of  
an EM field that allows you to break the Abbe resolution limit and  
something resulting from a specifically designed material structure
that would allow you to go well below the classic Boltzmann noise limit.

Classical physics doesn't allow you to build this gizmo:

https://en.wikipedia.org/wiki/Superlens

so maybe a noiseless system is possible as well?

    Best regards, Piotr

Re: Low voltage negative resistance oscillator design, lessons learned
On Thursday, 8 August 2019 20:59:26 UTC+1, Phil Hobbs  wrote:

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No they have negative noise, it's the negative of the problematic noise you'd expect :). Shame that doesn't help any.


NT

Re: Low voltage negative resistance oscillator design, lessons learned
On 08/08/19 17:52, bitrex wrote:
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The trigger circuit in Tek 4x5 era scopes was famously good. My
350MHz Tek 485 reliably triggers on a 1.1GHz signal. I suspect
it would go higher, but the amplitude is then only 0.2 divisions.

Step generators, of course; 50ps or less 0.4V into 50ohms is
achievable.

Re: Low voltage negative resistance oscillator design, lessons learned
Forgot a link:
 http://panteltje.com/pub//lighting_a_LED_with_a_candle_setup_IMG_3607.GIF

Re: Low voltage negative resistance oscillator design, lessons learned
On 8/8/19 2:53 PM, Jan Panteltje wrote:
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Ah, like the solar-powered flashlight!

Re: Low voltage negative resistance oscillator design, lessons learned
Jan Panteltje wrote:

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It should be possible to make a combo: the JFET one as a gate supply  
circuit for a very low R_DS_ON MOSFET for high-power applications.
Thermocouples can produce helluva amps, wasting them is a pity.
The JFET is switching voltage, the MOSFET is switching current, so to  
speak...

    Best regards, Piotr

Re: Low voltage negative resistance oscillator design, lessons learned
On a sunny day (Fri, 9 Aug 2019 22:49:10 +0200) it happened Piotr Wyderski

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Yes, done that too:
 
http://panteltje.com/pub/lighting_a_LED_with_a_candle_circuit_diagram_with_added_power_MOSFET.gif

The gate voltage at the JFET is enough to switch an IRLZ34N on / off.

Now all you need is some hot plutonium... for an RTG.

Magnifying lens, sun?
Efficiency better than a solar panel?

Gotto try:-)
  

Re: Low voltage negative resistance oscillator design, lessons learned
bitrex wrote:

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Give them a bulky tank circuit and they will go as low as 1MHz.
But what are you tryig to achieve?

    Best regards, Piotr

Re: Low voltage negative resistance oscillator design, lessons learned
On 09/08/2019 21:28, Piotr Wyderski wrote:
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There isn't a lower limit, tunnel diodes can do audio too.

piglet


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