Forums

phemt diode

Started by John Larkin May 10, 2021
The late lamanted ATF-50189 phemt made an amazing diode. 1 amp and
about 3 pF.

I tried a MiniCircuits SAV-541 as a diode.

https://www.dropbox.com/sh/0cgvrabjdichvu4/AAAGRgxUuWOEn0ULKFgjQK8da?dl=0

Cd is only about half a pF and Vf about 0.2. What's weird is that it's
very noisy in the negative-drain "forward" conduction direction. It's
the same at 20 MHz scope bandwidth, so it's not some GHz oscillation,
and it's a 1x probe anyhow.

Gotta look at this some more. I may have a use for a very fast, low
capacitance clamp.

There's another connection, drain to gate, but capacitance would be
higher. Cds and Cgs would be in parallel.

Phil's SAV model looks pretty good. It predicts the reverse drain
conduction spot on.

John Larkin wrote:
> > The late lamanted ATF-50189 phemt made an amazing diode. 1 amp and > about 3 pF. > > I tried a MiniCircuits SAV-541 as a diode. > > https://www.dropbox.com/sh/0cgvrabjdichvu4/AAAGRgxUuWOEn0ULKFgjQK8da?dl=0 > > Cd is only about half a pF and Vf about 0.2. What's weird is that it's > very noisy in the negative-drain "forward" conduction direction. It's > the same at 20 MHz scope bandwidth, so it's not some GHz oscillation, > and it's a 1x probe anyhow.
Typically, compound semiconductor devices that show a real lot of 1/f noise are gradually disassembling themselves. LEDs and diode lasers do the same thing--you can use anomalous 1/f noise as an indication of early failure.
> > Gotta look at this some more. I may have a use for a very fast, low > capacitance clamp. > > There's another connection, drain to gate, but capacitance would be > higher. Cds and Cgs would be in parallel. > > Phil's SAV model looks pretty good. It predicts the reverse drain > conduction spot on.
"Blind luck and bloody ignorance", as me old dad used to say. I'll take it. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
On Wed, 12 May 2021 10:43:37 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>John Larkin wrote: >> >> The late lamanted ATF-50189 phemt made an amazing diode. 1 amp and >> about 3 pF. >> >> I tried a MiniCircuits SAV-541 as a diode. >> >> https://www.dropbox.com/sh/0cgvrabjdichvu4/AAAGRgxUuWOEn0ULKFgjQK8da?dl=0 >> >> Cd is only about half a pF and Vf about 0.2. What's weird is that it's >> very noisy in the negative-drain "forward" conduction direction. It's >> the same at 20 MHz scope bandwidth, so it's not some GHz oscillation, >> and it's a 1x probe anyhow. > >Typically, compound semiconductor devices that show a real lot of 1/f >noise are gradually disassembling themselves. LEDs and diode lasers do >the same thing--you can use anomalous 1/f noise as an indication of >early failure.
It seems that there is oscillation beyond the range of my 500 MHz scope. At -0.2 volts on the gate and drain! I added a resistor in the gate, to ground, to see if the diode effect involves gate current. It doesn't seem to, at least until I hit the 12 volt drain breakdown.
> >> >> Gotta look at this some more. I may have a use for a very fast, low >> capacitance clamp. >> >> There's another connection, drain to gate, but capacitance would be >> higher. Cds and Cgs would be in parallel. >> >> Phil's SAV model looks pretty good. It predicts the reverse drain >> conduction spot on. > >"Blind luck and bloody ignorance", as me old dad used to say. > >I'll take it. ;)
Beats working.
> >Cheers > >Phil Hobbs
There was a circuit of a jfet-based oscillator dc/dc converter that ran down to 80 mV DC input, from a thermocouple maybe. I wonder if a phemt could do even better.
John Larkin wrote:
> On Wed, 12 May 2021 10:43:37 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> John Larkin wrote: >>> >>> The late lamanted ATF-50189 phemt made an amazing diode. 1 amp and >>> about 3 pF. >>> >>> I tried a MiniCircuits SAV-541 as a diode. >>> >>> https://www.dropbox.com/sh/0cgvrabjdichvu4/AAAGRgxUuWOEn0ULKFgjQK8da?dl=0 >>> >>> Cd is only about half a pF and Vf about 0.2. What's weird is that it's >>> very noisy in the negative-drain "forward" conduction direction. It's >>> the same at 20 MHz scope bandwidth, so it's not some GHz oscillation, >>> and it's a 1x probe anyhow. >> >> Typically, compound semiconductor devices that show a real lot of 1/f >> noise are gradually disassembling themselves. LEDs and diode lasers do >> the same thing--you can use anomalous 1/f noise as an indication of >> early failure. > > It seems that there is oscillation beyond the range of my 500 MHz > scope. At -0.2 volts on the gate and drain!
Not your upmarket 20 MHz LPF, then. ;)
> I added a resistor in the gate, to ground, to see if the diode effect > involves gate current. It doesn't seem to, at least until I hit the 12 > volt drain breakdown.
Okay, cool.
>>> Gotta look at this some more. I may have a use for a very fast, low >>> capacitance clamp. >>> >>> There's another connection, drain to gate, but capacitance would be >>> higher. Cds and Cgs would be in parallel. >>> >>> Phil's SAV model looks pretty good. It predicts the reverse drain >>> conduction spot on. >> >> "Blind luck and bloody ignorance", as me old dad used to say. >> >> I'll take it. ;) > > Beats working.
> > There was a circuit of a jfet-based oscillator dc/dc converter that > ran down to 80 mV DC input, from a thermocouple maybe. I wonder if a > phemt could do even better.
That was the "Joule thief" thing, right? Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
On 12/05/2021 23:48, Phil Hobbs wrote:
> John Larkin wrote: >> >> There was a circuit of a jfet-based oscillator dc/dc converter that >> ran down to 80 mV DC input, from a thermocouple maybe. I wonder if a >> phemt could do even better. > > That was the "Joule thief" thing, right? > > Cheers > > Phil Hobbs >
That was Jan Pantelje lighting a LED from a candle flame! piglet
On Thu, 13 May 2021 14:40:19 +0100, piglet <erichpwagner@hotmail.com>
wrote:

>On 12/05/2021 23:48, Phil Hobbs wrote: >> John Larkin wrote: >>> >>> There was a circuit of a jfet-based oscillator dc/dc converter that >>> ran down to 80 mV DC input, from a thermocouple maybe. I wonder if a >>> phemt could do even better. >> >> That was the "Joule thief" thing, right? >> >> Cheers >> >> Phil Hobbs >> > >That was Jan Pantelje lighting a LED from a candle flame! > >piglet >
His schematics, being unreadable, make good kindling. I draw on d-size velum and never throw them away. -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
John Larkin <jlarkin@highland_atwork_technology.com> wrote:

> On Wed, 12 May 2021 10:43:37 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >>John Larkin wrote: >>> >>> The late lamanted ATF-50189 phemt made an amazing diode. 1 amp and >>> about 3 pF.
[...]
> It seems that there is oscillation beyond the range of my 500 MHz > scope. At -0.2 volts on the gate and drain!
You can make a detector with a small loop of wire and a fast schottky or germanium diode. Just wave it near the circuit to spot any unusual radiation. There are plenty of radiation detectors on Amazon for finding bugs. I have no idea if they are any good. Linear Technology used to make logarithmic detectors with very wide bandwidth and good sensitivity. A SDRPlay RSP1A covers 1 KHz to 2 Ghz with 14 bit resolution and sensitivity in microvolts. It will find the weakest of oscillations. Your spectrum analyzer should be good for detecting oscillations. You should be able to pick up radiation from your celltower. This may confuse the readings from a parasitic oscillation. What happened to your SD-32? -- The best designs occur in the theta state. - sw
On Thu, 13 May 2021 16:55:31 -0000 (UTC), Steve Wilson
<spamme@not.com> wrote:

>John Larkin <jlarkin@highland_atwork_technology.com> wrote: > >> On Wed, 12 May 2021 10:43:37 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>>John Larkin wrote: >>>> >>>> The late lamanted ATF-50189 phemt made an amazing diode. 1 amp and >>>> about 3 pF. > >[...] > >> It seems that there is oscillation beyond the range of my 500 MHz >> scope. At -0.2 volts on the gate and drain! > >You can make a detector with a small loop of wire and a fast schottky or >germanium diode. Just wave it near the circuit to spot any unusual >radiation. > >There are plenty of radiation detectors on Amazon for finding bugs. I have >no idea if they are any good. > >Linear Technology used to make logarithmic detectors with very wide >bandwidth and good sensitivity. > >A SDRPlay RSP1A covers 1 KHz to 2 Ghz with 14 bit resolution and >sensitivity in microvolts. It will find the weakest of oscillations. > >Your spectrum analyzer should be good for detecting oscillations.
Right, that should suggest what's going on.
> >You should be able to pick up radiation from your celltower. This may >confuse the readings from a parasitic oscillation. > >What happened to your SD-32?
Still around. I have the 3 GHz sampling probe too, SD14 I think, that's a great e-field probe. But the sampling scopes need an external trigger. We have a 7 GHz LeCroy scope with fet probes too. -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
jlarkin@highlandsniptechnology.com wrote:
> On Thu, 13 May 2021 16:55:31 -0000 (UTC), Steve Wilson > <spamme@not.com> wrote: > >> John Larkin <jlarkin@highland_atwork_technology.com> wrote: >> >>> On Wed, 12 May 2021 10:43:37 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> John Larkin wrote: >>>>> >>>>> The late lamanted ATF-50189 phemt made an amazing diode. 1 amp and >>>>> about 3 pF. >> >> [...] >> >>> It seems that there is oscillation beyond the range of my 500 MHz >>> scope. At -0.2 volts on the gate and drain! >> >> You can make a detector with a small loop of wire and a fast schottky or >> germanium diode. Just wave it near the circuit to spot any unusual >> radiation. >> >> There are plenty of radiation detectors on Amazon for finding bugs. I have >> no idea if they are any good. >> >> Linear Technology used to make logarithmic detectors with very wide >> bandwidth and good sensitivity. >> >> A SDRPlay RSP1A covers 1 KHz to 2 Ghz with 14 bit resolution and >> sensitivity in microvolts. It will find the weakest of oscillations. >> >> Your spectrum analyzer should be good for detecting oscillations. > > Right, that should suggest what's going on. > >> >> You should be able to pick up radiation from your celltower. This may >> confuse the readings from a parasitic oscillation. >> >> What happened to your SD-32? > > Still around. I have the 3 GHz sampling probe too, SD14 I think, > that's a great e-field probe. But the sampling scopes need an external > trigger.
You can at least see hash if you use an arbitrary trigger frequency.
> > We have a 7 GHz LeCroy scope with fet probes too.
If you use a DC block, you can probably put those on your SA safely. I commonly use P6201 and P6249 FET probes on mine. (I have the matching TekProbe power supplies.) It's super easy to blow up the first mixer if you aren't careful about the DC! Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
On Thu, 13 May 2021 07:59:39 -0700, jlarkin@highlandsniptechnology.com
wrote:

>On Thu, 13 May 2021 14:40:19 +0100, piglet <erichpwagner@hotmail.com> >wrote: > >>On 12/05/2021 23:48, Phil Hobbs wrote: >>> John Larkin wrote: >>>> >>>> There was a circuit of a jfet-based oscillator dc/dc converter that >>>> ran down to 80 mV DC input, from a thermocouple maybe. I wonder if a >>>> phemt could do even better. >>> >>> That was the "Joule thief" thing, right? >>> >>> Cheers >>> >>> Phil Hobbs >>> >> >>That was Jan Pantelje lighting a LED from a candle flame! >> >>piglet >> > >His schematics, being unreadable, make good kindling.
I think they're great! Worthy of inclusion with the other great Dutch Masters. He sent me an original, complete with coffee and cigarette stains. One day I'll have to get around to framing it.
>I draw on d-size velum and never throw them away.
-- Best regards, Spehro Pefhany