Tunnel diode rectification

[Theo Markettos]

Does anyone still make tunnel diodes? I'm interested in having a play with
them. Particularly I'm interested in the fact that they pass a (relatively)
high current at low forward voltage, and in the forward direction the
forward current never goes to zero. Effectively I'd like to use it as a
rectifier with no forward voltage - where a Schottky won't do. It doesn't
matter that it has a low reverse breakdown voltage or valley point, as long
as the valley floor is above zero.

Is there a more modern device that will do this?

Thanks
Theo

--
Theo Markettos theo@markettos.org.uk
Clare Hall, Cambridge atm26@cam.ac.uk
CB3 9AL, UK http://www.markettos.org.uk/

 

[Tom Becker]

... a rectifier with no forward voltage...

With a conventional diode in its feedback loop, I believe, an opamp can
simulate a perfect rectifer. Would that do?

 

[Fred Abse]

On Mon, 07 Mar 2005 16:31:25 +0000, Theo Markettos wrote:

Does anyone still make tunnel diodes?

If you're prepared to pay megabucks, yes. Sometimes the turn up at
hamfests and swap meets.


I'm interested in having a play with

them. Particularly I'm interested in the fact that they pass a
(relatively) high current at low forward voltage,

A few milliamps, usually

and in the forward direction the
forward current never goes to zero. Effectively I'd like to use it as a
rectifier with no forward voltage - where a Schottky won't do. It
doesn't matter that it has a low reverse breakdown voltage or valley
point, as long as the valley floor is above zero.

The valley floor has to be above zero, otherwise the device would contain
a voltage source.

"Reverse breakdown" isn't really a property of tunnel diodes, they conduct
in the reverse direction more or less from zero.

Tunnel diodes don't rectify, in the sense that I take you to mean the
term.

Fun devices, though. Probably the fastest switching device there is. Quite
easy to generate pulses with picosecond rise times. If you're *really*
clever, you can amplify with them.

A word of warning: Don't try to test a tunnel diode with an ohmmeter. More
of them have been damaged doing that than ever failed in service, and even
if the device survives, it'll tell you nothing, since they conduct in both
directions.


--
Then there's duct tape ...
(Garrison Keillor)

 

[mike]

Fred Abse wrote:

On Mon, 07 Mar 2005 16:31:25 +0000, Theo Markettos wrote:


Does anyone still make tunnel diodes?


If you're prepared to pay megabucks, yes. Sometimes the turn up at
hamfests and swap meets.


I'm interested in having a play with

them. Particularly I'm interested in the fact that they pass a
(relatively) high current at low forward voltage,


A few milliamps, usually


and in the forward direction the
forward current never goes to zero. Effectively I'd like to use it as a
rectifier with no forward voltage - where a Schottky won't do. It
doesn't matter that it has a low reverse breakdown voltage or valley
point, as long as the valley floor is above zero.


The valley floor has to be above zero, otherwise the device would contain
a voltage source.

"Reverse breakdown" isn't really a property of tunnel diodes, they conduct
in the reverse direction more or less from zero.

Tunnel diodes don't rectify, in the sense that I take you to mean the
term.

Fun devices, though. Probably the fastest switching device there is. Quite
easy to generate pulses with picosecond rise times. If you're *really*
clever, you can amplify with them.

A word of warning: Don't try to test a tunnel diode with an ohmmeter. More
of them have been damaged doing that than ever failed in service, and even
if the device survives, it'll tell you nothing, since they conduct in both
directions.

There's a variant of the tunnel diode called a back or backward diode.
Think of it as a TD with extremely low peak current. Hook it up
backwards and it makes a low forward-drop rectifier with a reverse
breakdown of half a volt or so.

Unless you need a fast rise pulse, stay away from tunnel diodes.
Alternate technology has overtaken them for most other uses.
mike

--
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with links. Delete this sig when replying.
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[Watson A.Name - \"Watt Su]

"Theo Markettos" <theom+news@chiark.greenend.org.uk> wrote in message
news:rpi*3bYIq@news.chiark.greenend.org.uk...

Does anyone still make tunnel diodes? I'm interested in having a play
with
them. Particularly I'm interested in the fact that they pass a
(relatively)
high current at low forward voltage, and in the forward direction the
forward current never goes to zero. Effectively I'd like to use it as
a
rectifier with no forward voltage - where a Schottky won't do. It
doesn't
matter that it has a low reverse breakdown voltage or valley point, as
long
as the valley floor is above zero.

Is there a more modern device that will do this?

Yes, a regular power FET will act as a rectifier with lower V drop than
a Schottky. See the intro on P.6.
http://www.onsemi.com/pub/Collateral/NIS6111-D.PDF1

Thanks
Theo
--
Theo Markettos theo@markettos.org.uk
Clare Hall, Cambridge atm26@cam.ac.uk
CB3 9AL, UK http://www.markettos.org.uk/

 

[Watson A.Name - \"Watt Su]

"Fred Abse" <excretatauris@cerebrumconfus.it> wrote in message
newsan.2005.03.07.19.25.29.738334@cerebrumconfus.it...

On Mon, 07 Mar 2005 16:31:25 +0000, Theo Markettos wrote:

[snip]

Fun devices, though. Probably the fastest switching device there is.
Quite
easy to generate pulses with picosecond rise times. If you're *really*
clever, you can amplify with them.

When I experimented with them, they seemed to have one nasty habit.
They took every bit of stray inductance and capacitance and turned them
into a delay line. Instead of oscillating with a sine wave, they
decided that they wanted to do square waves instead. :-/

A word of warning: Don't try to test a tunnel diode with an ohmmeter.
More
of them have been damaged doing that than ever failed in service, and
even
if the device survives, it'll tell you nothing, since they conduct in
both
directions.
--

 

[Fred Abse]

On Mon, 07 Mar 2005 20:13:56 -0800, Watson A.Name - "Watt Sun, the Dark
Remover" wrote:

"Fred Abse" <excretatauris@cerebrumconfus.it> wrote in message
newsan.2005.03.07.19.25.29.738334@cerebrumconfus.it...
On Mon, 07 Mar 2005 16:31:25 +0000, Theo Markettos wrote:

[snip]

Fun devices, though. Probably the fastest switching device there is.
Quite
easy to generate pulses with picosecond rise times. If you're *really*
clever, you can amplify with them.

When I experimented with them, they seemed to have one nasty habit.
They took every bit of stray inductance and capacitance and turned them
into a delay line. Instead of oscillating with a sine wave, they
decided that they wanted to do square waves instead. :-/

Yep. They do that. If you want sine waves, you need a high Q tuned
circuit, and play with the bias so as it's on the middle of the negative
slope (the bit you can't see on a curve tracer, 'cos it's too fast).
RC circuits just make them switch.

Cavities go very well.

--
Then there's duct tape ...
(Garrison Keillor)

 

[Fred Abse]

On Mon, 07 Mar 2005 12:43:06 -0800, mike wrote:

There's a variant of the tunnel diode called a back or backward diode.
Think of it as a TD with extremely low peak current. Hook it up
backwards and it makes a low forward-drop rectifier with a reverse
breakdown of half a volt or so.

Seen (aka burnt out) a few of those in mixers in my time

--
Then there's duct tape ...
(Garrison Keillor)

 

[Theo Markettos]

Fred Abse <excretatauris@cerebrumconfus.it> wrote:

On Mon, 07 Mar 2005 16:31:25 +0000, Theo Markettos wrote:
The valley floor has to be above zero, otherwise the device would contain
a voltage source.

True, good point.

"Reverse breakdown" isn't really a property of tunnel diodes, they conduct
in the reverse direction more or less from zero.

Tunnel diodes don't rectify, in the sense that I take you to mean the
term.

Am I misreading something from the graph at:
http://www.americanmicrosemi.com/tutorials/tunneldiode.htm

which seems to suggest that they're basically like a Zener except the
tunnelling current means they have a lower resistance at low applied
voltages than at medium ones? I suppose the problem is lack of scale on the
left/lower parts of the graph. It does seem to suggest that they're
actually better at conducting in the reverse direction than the forward
direction - is this true? I can't seem to find any datasheets on these
diodes.

My interest is for a crystal radio, where the forward voltage drop of a
silicon, Schottky or germanium diode means you lose a lot of signal, but
power isn't available. I was wondering whether a tunnel diode might be more
efficient? Are there any other types of diode that might do the trick
instead?

Thanks
Theo

--
Theo Markettos theo@markettos.org.uk
Clare Hall, Cambridge atm26@cam.ac.uk
CB3 9AL, UK http://www.markettos.org.uk/

 

[mike]

Theo Markettos wrote:

Fred Abse <excretatauris@cerebrumconfus.it> wrote:

On Mon, 07 Mar 2005 16:31:25 +0000, Theo Markettos wrote:
The valley floor has to be above zero, otherwise the device would contain
a voltage source.


True, good point.


"Reverse breakdown" isn't really a property of tunnel diodes, they conduct
in the reverse direction more or less from zero.

Tunnel diodes don't rectify, in the sense that I take you to mean the
term.


Am I misreading something from the graph at:
http://www.americanmicrosemi.com/tutorials/tunneldiode.htm

which seems to suggest that they're basically like a Zener except the
tunnelling current means they have a lower resistance at low applied
voltages than at medium ones? I suppose the problem is lack of scale on the
left/lower parts of the graph. It does seem to suggest that they're
actually better at conducting in the reverse direction than the forward
direction - is this true? I can't seem to find any datasheets on these
diodes.

My interest is for a crystal radio, where the forward voltage drop of a
silicon, Schottky or germanium diode means you lose a lot of signal, but
power isn't available. I was wondering whether a tunnel diode might be more
efficient? Are there any other types of diode that might do the trick
instead?

Thanks
Theo

How about a Germanium point-contact diode?
I've read reports that you can get the best performance with a real
Galena Xtal and real cat whisker...as long as you're willing to futz
with it.
You often get better results if the Subject line reflects your actual
objectives. Unlikely that a cat-whisker expert is gonna read a tunnel
diode post.
mike

--
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
..
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/

 

[Watson A.Name - \"Watt Su]

"Theo Markettos" <theom+news@chiark.greenend.org.uk> wrote in message
newsux*Rw8Iq@news.chiark.greenend.org.uk...

Fred Abse <excretatauris@cerebrumconfus.it> wrote:
On Mon, 07 Mar 2005 16:31:25 +0000, Theo Markettos wrote:
The valley floor has to be above zero, otherwise the device would
contain
a voltage source.

True, good point.

"Reverse breakdown" isn't really a property of tunnel diodes, they
conduct
in the reverse direction more or less from zero.

Tunnel diodes don't rectify, in the sense that I take you to mean
the
term.

Am I misreading something from the graph at:
http://www.americanmicrosemi.com/tutorials/tunneldiode.htm

which seems to suggest that they're basically like a Zener except the
tunnelling current means they have a lower resistance at low applied
voltages than at medium ones? I suppose the problem is lack of scale
on the
left/lower parts of the graph. It does seem to suggest that they're
actually better at conducting in the reverse direction than the
forward
direction - is this true? I can't seem to find any datasheets on
these
diodes.

My interest is for a crystal radio, where the forward voltage drop of
a
silicon, Schottky or germanium diode means you lose a lot of signal,
but
power isn't available. I was wondering whether a tunnel diode might
be more
efficient? Are there any other types of diode that might do the trick
instead?

Thanks
Theo

--

You're supposed to do it like this.
http://www.oldradioworld.de/gollum/dt.htm

These use a separate diode to rectify and filter the RF, then power the
amplifier with it. So you are getting free power from the RF in the
air. Just remember to use a long wire, the longer the better.
Germanium diodes will rectify with a drop of only a quarter volt.

Or you can use a solar cell that puts out a few volts to furnish the
power to amplify the RF and/or AF. You can also buy one of the radios
that has a solar cell and crank built in, and will run off the crank
generator for several minutes or off the solar cells if it's sunny.

 

[Fred Abse]

On Wed, 09 Mar 2005 15:30:54 +0000, Theo Markettos wrote:

Am I misreading something from the graph at:
http://www.americanmicrosemi.com/tutorials/tunneldiode.htm

I think you're looking at the superimposed "conventional" characteristic,
and implying reverse blocking. Tunnel diodes conduct in reverse more or
less from zero. It isn't a very good idea to apply reverse bias as more
than a few milliamps will destroy them.

Tunnel diodes exhibit useful properties (ie. negative resistance) in the
forward direction only.

which seems to suggest that they're basically like a Zener

A Zener has a defined reverse breakdown voltage and is generally used
reverse-biased. A tunnel diode has a reverse breakdown voltage of
approximately zero.

except the

tunnelling current means they have a lower resistance at low applied
voltages than at medium ones? I suppose the problem is lack of scale on the
left/lower parts of the graph. It does seem to suggest that they're
actually better at conducting in the reverse direction than the forward
direction - is this true?

Yes, but they're never used in the reverse direction, nothing useful
there. It's the negative resistance portion between the peak and valley
that makes them useful. With a resistive load, increasing forward voltage
through the peak point will result in a current step with picosecond rise
time. Alternatively, you can use the negative resistance to overcome the
losses of a tuned circuit, and oscillation will occur. That technique is
usable at many GHz.

I can't seem to find any datasheets on these
diodes.

There was *some* data in the old GE "Transistor Manual", if you can find
a copy. Most information was published in the 1960s, and is probably out
of print, now. They were used extensively as trigger switches in high-end
oscilloscopes by Tektronix and HP.

My interest is for a crystal radio, where the forward
voltage drop of a
silicon, Schottky or germanium diode means you lose a lot of signal, but
power isn't available. I was wondering whether a tunnel diode might be
more efficient?

It would certainly oscillate, but I guess a transmitter isn't what you
want

Are there any other types of diode that might do the

trick instead?

There's a thing called the backward diode, which is similar in principle
to the tunnel diode, but which is designed as a (microwave) detector.
They're probably as difficult to find as pork chops in a synagogue

Is it worth going to all that trouble for a crystal receiver? Selectivity
is just too poor for today's crowded spectrum.

--
Then there's duct tape ...
(Garrison Keillor)

 

[Watson A.Name - \"Watt Su]

"Fred Abse" <excretatauris@cerebrumconfus.it> wrote in message
newsan.2005.03.10.22.53.41.33195@cerebrumconfus.it...

On Wed, 09 Mar 2005 15:30:54 +0000, Theo Markettos wrote:

[snip]

My interest is for a crystal radio, where the forward
voltage drop of a
silicon, Schottky or germanium diode means you lose a lot of signal,
but
power isn't available. I was wondering whether a tunnel diode might
be
more efficient?

It would certainly oscillate, but I guess a transmitter isn't what you
want

Are there any other types of diode that might do the
trick instead?

There's a thing called the backward diode, which is similar in
principle
to the tunnel diode, but which is designed as a (microwave) detector.
They're probably as difficult to find as pork chops in a synagogue

Is it worth going to all that trouble for a crystal receiver?
Selectivity
is just too poor for today's crowded spectrum.

That's a good point. And it takes a decent long wire antenna, which is
usually larger than most dwellings can accommodate.

> --