an electronish puzzle

[Ken Smith]

In article <s3q04198rsndnf507kptm9qic6oj2gsflt@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
[....]

OK, but you're going to have to resolve nanoamps in milliseconds.
Sounds like a project.

You betcha

1nA * 1mS = 1pC

Charging the junction capacitances is going to cause a current spike that
may be bigger than the value to be measured. This makes for some
instumentation problems. The fact that the capcitances are not linear
makes life even more interesting.

OR:

Figure out some way to make an electric heater keep the junction
temperature constant. The semiconductor to case resistance is a linear
effect. The effective location of the heat source within that
semiconductor may move a little when the current changes, but I think that
that is going to be too small of an effect to worry about.





--
--
kensmith@rahul.net forging knowledge

 

[John Larkin]

On Thu, 24 Mar 2005 09:13:53 GMT, Fred Bloggs <nospam@nospam.com>
wrote:

John Larkin wrote:
On Wed, 23 Mar 2005 08:02:13 GMT, Fred Bloggs <nospam@nospam.com
wrote:


There is more of your narcissism- like who cares what you do or do not
respect. And I don't know why you would have any respect for me- I
certainly have none for you- this should be clear to you by now- what's
there about you to respect or even be interested in.


Ah, but then you haven't seen my collection of colorful little
earthenware coffee pots.

John


Typical queen response....

Well, face it Fred, if we'd wanted to be admired for our machismo we
should have been lumberjacks or fighter pilots or something. People
who spend their days clicking mice and probing TSOPs under microscopes
are hardly going to be confused with Bruce Lee. I think that's why so
many Silicon Valley techs dress up like cowboys and have lunch at
stripper bars... just to prove they're not soldering-iron-armed
pansies. (Their loss; those places always have bad, expensive food.)

Hmmm... maybe that's why I like milling machines and lathes so much.
There's nothing like hogging out a big block of 6062 now and then to
make a guy feel manly. The smell of cutting fluid drives women crazy.

But I digress. Richard Feynman wrote a book on this very subject. You
wouldn't have liked him, either.

John

 

[John Larkin]

On Thu, 24 Mar 2005 15:21:27 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <s3q04198rsndnf507kptm9qic6oj2gsflt@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
[....]
OK, but you're going to have to resolve nanoamps in milliseconds.
Sounds like a project.


You betcha

1nA * 1mS = 1pC

Charging the junction capacitances is going to cause a current spike that
may be bigger than the value to be measured. This makes for some
instumentation problems. The fact that the capcitances are not linear
makes life even more interesting.

Actually, if you just dump the collector current into a 1M scope
input, there'd be numbers like a quarter of a volt in this case,
plenty of signal. Tau might be in the 10s of microseconds, so
millisecond thermals (should there be thermals!) should be obvious.

Once the b-e junction is zenered, all the transients should be over
pretty quick.


John

 

[Larry Brasfield]

"Ken Smith" <kensmith@green.rahul.net> wrote in
message news:d1ultn$8gp$1@blue.rahul.net...

In article <s3q04198rsndnf507kptm9qic6oj2gsflt@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
[....]
OK, but you're going to have to resolve nanoamps in milliseconds.
Sounds like a project.

You betcha

1nA * 1mS = 1pC

Charging the junction capacitances is going to cause a current spike that
may be bigger than the value to be measured. This makes for some
instumentation problems.

Quite so. I plan to use single frequency excitation. That makes
extraction of signal from noisy sample data a little easier too.

The fact that the capcitances are not linear
makes life even more interesting.

Well, they are nonlinear, but the voltages across
both junctions are or can be held pretty constant.
(I plan to use a conventional, low Z-in photoamp
circuit to collect the collector output current.)

OR:

Figure out some way to make an electric heater keep the junction
temperature constant. The semiconductor to case resistance is a linear
effect. The effective location of the heat source within that
semiconductor may move a little when the current changes, but I think that
that is going to be too small of an effect to worry about.

If I read that correctly, you mean to permit a DC
measurement of the b-e zenering effect, separated
from the temperature effect, by holding some
temperature within the device constant under DC
conditions. (If it was transient or AC conditions,
the cure would be harder than the problem.)

One problem with that approach is that there are
temperature gradients within the device when you
dissipate power at/around/in a junction, but the
"bez" effects are not necessarily occuring at the
same places as the dissipation. For example,
the temperature effect on c-b leakage itself
occurs throughout the base region and in the
c-b depletion region. You would need to hold
those temperatures constant.

With the AC excitation at a suitable frequency, both
the capacitance effect (due to junction voltages not
being constant) and the thermal effect have a fortunate
phase relationship to the "bez" effect, which has no
way to be slow enough to be anything but in phase
with the excitation. (That's just "theory", of course;
the lab may well play some of its usual pranks.)

In my work on a precision square wave generator
one time, I found that junction scale thermal tails
occur with about half mS timescales for small RF
transistors. So I'm thinking 10 to 30 KHz will be
a suitable frequency for getting the thermal effects
(which are slower because not at one junction) to
appear with a 90 degree phase shift.

I will (and do) appreciate any predictions as to
problems with the AC excitation approach.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Rich Grise]

On Thu, 24 Mar 2005 08:17:39 -0800, John Larkin wrote:

On Thu, 24 Mar 2005 09:13:53 GMT, Fred Bloggs <nospam@nospam.com

Well, face it Fred, if we'd wanted to be admired for our machismo we
should have been lumberjacks or fighter pilots or something. People
who spend their days clicking mice and probing TSOPs under microscopes
are hardly going to be confused with Bruce Lee.

Once, in the drunk tank, some guy said I looked like Chuck Norris. ;-)

Cheers!
Rich

 

[Larry Brasfield]

"Rich Grise" <richgrise@example.net> wrote in message newsan.2005.03.24.19.37.40.122551@example.net...

On Thu, 24 Mar 2005 08:17:39 -0800, John Larkin wrote:

On Thu, 24 Mar 2005 09:13:53 GMT, Fred Bloggs <nospam@nospam.com

Well, face it Fred, if we'd wanted to be admired for our machismo we
should have been lumberjacks or fighter pilots or something. People
who spend their days clicking mice and probing TSOPs under microscopes
are hardly going to be confused with Bruce Lee.

Once, in the drunk tank, some guy said I looked like Chuck Norris. ;-)

Do you mean in "the dunk tank" with your shirt
off or wet? Or do you mean "jail on public
drunkeness charges"? (I ask only because you do
not seem the sort to be found in the gutter.)

(And if you were gaffing, do take a point. ;-)

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Guy Macon]

Rich Grise wrote:

On Thu, 24 Mar 2005 08:17:39 -0800, John Larkin wrote:

On Thu, 24 Mar 2005 09:13:53 GMT, Fred Bloggs <nospam@nospam.com

Well, face it Fred, if we'd wanted to be admired for our machismo we
should have been lumberjacks or fighter pilots or something. People
who spend their days clicking mice and probing TSOPs under microscopes
are hardly going to be confused with Bruce Lee.

Once, in the drunk tank, some guy said I looked like Chuck Norris. ;-)

Nah, Chuck Norris isn't as good looking as you are.

 

[Rich Grise]

On Thu, 24 Mar 2005 11:45:31 -0800, Larry Brasfield wrote:

"Rich Grise" <richgrise@example.net> wrote in message

Once, in the drunk tank, some guy said I looked like Chuck Norris. ;-)

Do you mean in "the dunk tank" with your shirt
off or wet? Or do you mean "jail on public
drunkeness charges"? (I ask only because you do
not seem the sort to be found in the gutter.)

(And if you were gaffing, do take a point. ;-)

Jail for getting caught driving while having over 0.10% blood alcohol
content. (I don't get "drunk" until about 0.25%.) Actually, it was
only "setting off the cop's breath box". And I wouldn't have got caught
if I'd checked the taillights. )-;

Cheers!
Rich

 

[Ken Smith]

In article <boq5419fplseu9l1u9mvo93ao3hm4opa7m@4ax.com>,
John Larkin <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:

On Thu, 24 Mar 2005 15:21:27 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <s3q04198rsndnf507kptm9qic6oj2gsflt@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
[....]
OK, but you're going to have to resolve nanoamps in milliseconds.
Sounds like a project.


You betcha

1nA * 1mS = 1pC

Charging the junction capacitances is going to cause a current spike that
may be bigger than the value to be measured. This makes for some
instumentation problems. The fact that the capcitances are not linear
makes life even more interesting.


Actually, if you just dump the collector current into a 1M scope
input, there'd be numbers like a quarter of a volt in this case,
plenty of signal. Tau might be in the 10s of microseconds, so
millisecond thermals (should there be thermals!) should be obvious.

It is still less than the ideal situation. My main concern would be:

If you do it this way, the spike from charging the C-E capacitance will be
something like 8V. This means the full scale of the scope must be about
20 times the signal to be measured. This is losing you the top 4 bits of
the number.

With a 12 bit converter this would not be a show stopper but it is still
not nice to lose those bits.


Considering the time constants:

The tail after this has lets say a 10uS TC. If we want to measure to 1%,
we need to wait about:

10uS * -ln(0.01 * 0.25/8) = 80uS

This number is much less of a problem since the juction is not likely to
change temperature hugely in that much time.

Once the b-e junction is zenered, all the transients should be over
pretty quick.

Yes, I agree with that.

--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <7mD0e.20$TJ1.579@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:

"Ken Smith" <kensmith@green.rahul.net> wrote in
message news:d1ultn$8gp$1@blue.rahul.net...
In article <s3q04198rsndnf507kptm9qic6oj2gsflt@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
[....]
OK, but you're going to have to resolve nanoamps in milliseconds.
Sounds like a project.

You betcha

1nA * 1mS = 1pC

Charging the junction capacitances is going to cause a current spike that
may be bigger than the value to be measured. This makes for some
instumentation problems.

Quite so. I plan to use single frequency excitation. That makes
extraction of signal from noisy sample data a little easier too.

How are you going to deal with the non-linearities of the capacitances and
the fact that they don't have a zero damping factor? Using a single
frequency seems like a bad idea because it allows confounding variables
into the issue.

The fact that the capcitances are not linear
makes life even more interesting.

Well, they are nonlinear, but the voltages across
both junctions are or can be held pretty constant.
(I plan to use a conventional, low Z-in photoamp
circuit to collect the collector output current.)

What will happen to the capacitance of the E-B juntion as the zener
current changes?

OR:

Figure out some way to make an electric heater keep the junction
temperature constant. The semiconductor to case resistance is a linear
effect. The effective location of the heat source within that
semiconductor may move a little when the current changes, but I think that
that is going to be too small of an effect to worry about.

If I read that correctly, you mean to permit a DC
measurement of the b-e zenering effect, separated
from the temperature effect, by holding some
temperature within the device constant under DC
conditions. (If it was transient or AC conditions,
the cure would be harder than the problem.)

One problem with that approach is that there are
temperature gradients within the device when you
dissipate power at/around/in a junction, but the
"bez" effects are not necessarily occuring at the
same places as the dissipation. For example,
the temperature effect on c-b leakage itself
occurs throughout the base region and in the
c-b depletion region. You would need to hold
those temperatures constant.

I'll remind you that I said:

Newsgroups: sci.electronics.design
Subject: Re: an electronish puzzle
In article <d1ultn$8gp$1@blue.rahul.net>,
Ken Smith <kensmith@green.rahul.net> wrote:
[...]

temperature constant. The semiconductor to case resistance is a linear
effect. The effective location of the heat source within that
semiconductor may move a little when the current changes, but I think that
that is going to be too small of an effect to worry about.

I still think this is true.

With the AC excitation at a suitable frequency, both
the capacitance effect (due to junction voltages not
being constant) and the thermal effect have a fortunate
phase relationship to the "bez" effect, which has no
way to be slow enough to be anything but in phase
with the excitation.

The capacitances interacting with each other form capacitive
voltage dividers. The E-B junction has a low and real impedance when it
is zenered. This makes a path for the capacitance to carry an in phase AC
component to the collector lead.

--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <phi041165n4bvhunegkkfo0f60sne9o7pr@4ax.com>,
John Larkin <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:

On Tue, 22 Mar 2005 15:16:50 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <9a4u319497u9jbn4ljfk5afjobp7oc3dq8@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
[...]
So, why can't a poor engineer buy NTC surface mount ceramic capacitors
anywhere? That's the real mystery.

SMT inductors often have a NTC. How about putting one in series with the
capacitor?



The inductor I'm using in this oscillator, a 1008 surface-mount, has
(apparently) a strong positive TC. All the aircore inductors I've used
had positive TCs; I guess they just expand with temperature, and
bigger diameter makes more L. This is only 150 nH, so a
temperature-compensating core is probably out of the question.

I assume you are running above 100MHz. In general cores become near
useless at those frequencies. You may still be able to find some with
cores. It would be interesting to know if their tempco could be counted
on.

--
--
kensmith@rahul.net forging knowledge

 

[John Larkin]

On Fri, 25 Mar 2005 03:38:53 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <boq5419fplseu9l1u9mvo93ao3hm4opa7m@4ax.com>,
John Larkin <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:
On Thu, 24 Mar 2005 15:21:27 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <s3q04198rsndnf507kptm9qic6oj2gsflt@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
[....]
OK, but you're going to have to resolve nanoamps in milliseconds.
Sounds like a project.


You betcha

1nA * 1mS = 1pC

Charging the junction capacitances is going to cause a current spike that
may be bigger than the value to be measured. This makes for some
instumentation problems. The fact that the capcitances are not linear
makes life even more interesting.


Actually, if you just dump the collector current into a 1M scope
input, there'd be numbers like a quarter of a volt in this case,
plenty of signal. Tau might be in the 10s of microseconds, so
millisecond thermals (should there be thermals!) should be obvious.

It is still less than the ideal situation. My main concern would be:

If you do it this way, the spike from charging the C-E capacitance will be
something like 8V. This means the full scale of the scope must be about
20 times the signal to be measured. This is losing you the top 4 bits of
the number.

But the transition from zero emitter current to lots of current will
happen in 0.1 volts delta Vbe or less. And the base is an ideal shield
between the emitter and the collector, which is why people like
cascodes (hell, you could *do* it as a cascode.)

So you could easily make a pulse that goes from Ie = 0 to Ie = 10s of
mA, with almost no capacitive coupling to the collector/scope. And, as
I noted, the recovery time constant will be fast. There's plenty of
signal, so shunt the scope with a 100K resistor (or a 10K if you have
something exotic like a 7A22 handy) and really bash the tau.

This is an easy (if unnecessary) measurement to make. With a scope, a
pulse generator, a power supply, and a resistor or two, it could be
done in minutes.

John

 

[John Larkin]

On Fri, 25 Mar 2005 03:56:58 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <phi041165n4bvhunegkkfo0f60sne9o7pr@4ax.com>,
John Larkin <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:
On Tue, 22 Mar 2005 15:16:50 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <9a4u319497u9jbn4ljfk5afjobp7oc3dq8@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
[...]
So, why can't a poor engineer buy NTC surface mount ceramic capacitors
anywhere? That's the real mystery.

SMT inductors often have a NTC. How about putting one in series with the
capacitor?



The inductor I'm using in this oscillator, a 1008 surface-mount, has
(apparently) a strong positive TC. All the aircore inductors I've used
had positive TCs; I guess they just expand with temperature, and
bigger diameter makes more L. This is only 150 nH, so a
temperature-compensating core is probably out of the question.

I assume you are running above 100MHz. In general cores become near
useless at those frequencies. You may still be able to find some with
cores. It would be interesting to know if their tempco could be counted
on.

50 MHz, using a 1008 surface-mount coil with a ceramic body. The boys
have just about got me convinced to use an SPI temp sensor, some math
in the uP, a DAC, and a varicap to zap the tempco. Given how much
trouble I'm having getting NTC caps, I suppose they're right, grumble.
Brute force wins again.

John

 

[John Larkin]

On Mon, 21 Mar 2005 15:39:06 -0800, "Larry Brasfield"
<donotspam_larry_brasfield@hotmail.com> wrote:

You wrote earlier:
It's apparently linear up to Ie of 10 mA, all i did,
at which time Ic is up to 260 nA.
If it was not exponential, as the temperature effect
would cause, then either your transistor is going
into avalanche or the mechanism at work is one
which has eluded everybody here (who played),
including myself, along with a number of bright
interviewees including one with a PhD obtained
after his work in novel semiconductor devices.
I will soon be asking him again about this puzzle.
For all I know, there could be another, parallel
effect in addition to all the tunneling.

I'm an engineer, so when theory collides with parts, I trust the
parts.


"One experiment is worth a thousand expert opinions."

- Werner Von Braun.


John

 

[Larry Brasfield]

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote
in message news:k6pu311u2cuh3nn9l7520oe9dpqu0na7s9@4ax.com...

On Mon, 21 Mar 2005 15:39:06 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:


You wrote earlier:
It's apparently linear up to Ie of 10 mA, all i did,
at which time Ic is up to 260 nA.
If it was not exponential, as the temperature effect
would cause, then either your transistor is going
into avalanche or the mechanism at work is one
which has eluded everybody here (who played),
including myself, along with a number of bright
interviewees including one with a PhD obtained
after his work in novel semiconductor devices.
I will soon be asking him again about this puzzle.
For all I know, there could be another, parallel
effect in addition to all the tunneling.

I'm an engineer, so when theory collides with parts, I trust the
parts.

So do I, with certain reservations.

What seems to have gotten lost here is pretty
simple, so I will state it more succintly:

1. "The" theory says that the 1st order effect
is 0, no change in observed collector current.

2. There are 2nd order effects. They are hard
to quantify, (especially for people like us who
do not live and breath that sort of stuff).

3. You have observed a very small change in
collector current, linear to some degree, when
performing the experiment with a real part.

Do you see, in that set of statements, any
collision between "theory" and your parts?

"One experiment is worth a thousand expert opinions."

- Werner Von Braun.

Ok. But the right experts can avoid the need for some
experiments and inform the design of others.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Jim Thompson]

On Tue, 22 Mar 2005 07:41:47 -0800, John Larkin
<jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:

On Tue, 22 Mar 2005 13:34:47 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Fred Bartoli
fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote
(in <4240112b$0$2080$636a15ce@news.free.fr&gt about 'an electronish
puzzle', on Tue, 22 Mar 2005:

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> a écrit dans le message de
news:UhnOqPT9YAQCFwz5@jmwa.demon.co.uk...
I read in sci.electronics.design that Fred Bartoli
fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote
(in <423fe4ea$0$2048$636a15ce@news.free.fr&gt about 'an electronish
puzzle', on Tue, 22 Mar 2005:
Maybe you can buy a tin of violet paint?

Violet is N750. OK, making 1/3 of the capacitance N750 and the rest
NP0/COG would do. But yellow paint gets you N220. (;-)

So he has to get the missing 30ppm by carefully hand selecting NPO?

What a paint in the arse...


Actually, he still needs a sniff of N750 to *increase* the overall TC.
But yes, it was a PITA correcting drift this way, especially as you had
to wait at least an hour to see the results of any change.


"Pain in the arse" is a good assessment. The current product uses a
varicap driven by an LM45 temp sensor, a couple of opamps, and a
trimpot. Even without soldering, adjusting the tc is a huge, tedious
nuisance. Now I want to make a really tiny version, so an NTC cap
would be ideal. There's a huge matrix of possibilities combining fixed
caps and NTCs; NTCs are theoretically available from N220 to N5600.
Disc NTC caps are still somewhat available, but it's hard to get
surface-mounts unless you want to buy a million, which makes
experimenting problematical.

If I could get the TC down from -125 to, say, +-40 maybe, it would
solve my problem.

John

Years ago I designed a scheme that tested an oven-less crystal
oscillator over several days.

A DAC was used to adjust the varicap voltage to bring the oscillator
frequency dead-on.

Data was stored in a ROM that was addressed dependent on temperature.

Oven performance without oven. <http://saunders-assoc.com/index.html>

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Larry Brasfield]

"Ken Smith" <kensmith@green.rahul.net> wrote in
message news:d201na$ag6$2@blue.rahul.net...

In article <7mD0e.20$TJ1.579@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:
"Ken Smith" <kensmith@green.rahul.net> wrote in
message news:d1ultn$8gp$1@blue.rahul.net...
....
1nA * 1mS = 1pC

Charging the junction capacitances is going to cause a current spike that
may be bigger than the value to be measured. This makes for some
instumentation problems.

Quite so. I plan to use single frequency excitation. That makes
extraction of signal from noisy sample data a little easier too.

How are you going to deal with the non-linearities of the capacitances and
the fact that they don't have a zero damping factor?

Can you elaborate on that? (maybe after considering
the discussion on non-linearity as developed below)
The "damping factor" issue completely escapes me.

Using a single
frequency seems like a bad idea because it allows confounding variables
into the issue.

It seems to me that it allows better separation of the
confounding variables, at least the ones I know of.
Which variables do you believe are more confounding
with single frequency excitation? (Mind you, I am
not saying only one frequency is to be used in the
experiment -- just that they are used one at a time.)

The fact that the capcitances are not linear
makes life even more interesting.

Well, they are nonlinear, but the voltages across
both junctions are or can be held pretty constant.
(I plan to use a conventional, low Z-in photoamp
circuit to collect the collector output current.)

What will happen to the capacitance of the E-B juntion as the zener
current changes?

I don't think it is sensitive to current per-se. To get
that current change, the voltage must change. And
that modulates the depletion region width, which of
course is as non-linear as the doping profile is non-
constant (away from the junction itself).

I agree that non-linearity can be a real complication.
But its impact can be reduced by using the AC
excitation approach, with signals made small enough.

....

Figure out some way to make an electric heater keep the junction
temperature constant. The semiconductor to case resistance is a linear
effect. The effective location of the heat source within that
semiconductor may move a little when the current changes, but I think that
that is going to be too small of an effect to worry about.

If I read that correctly, you mean to permit a DC
measurement of the b-e zenering effect, separated
from the temperature effect, by holding some
temperature within the device constant under DC
conditions. (If it was transient or AC conditions,
the cure would be harder than the problem.)

One problem with that approach is that there are
temperature gradients within the device when you
dissipate power at/around/in a junction, but the
"bez" effects are not necessarily occuring at the
same places as the dissipation. For example,
the temperature effect on c-b leakage itself
occurs throughout the base region and in the
c-b depletion region. You would need to hold
those temperatures constant.

I'll remind you that I said:
[cite cut]
temperature constant. The semiconductor to case resistance is a linear
effect. The effective location of the heat source within that
semiconductor may move a little when the current changes, but I think that
that is going to be too small of an effect to worry about.

I still think this is true.

I think so too. I did not mean to contravene that,
but to bring up a larger difficulty with trying to hold
some relevant temperature constant. I will try to
state the point less obliquely.

The heat generated by the b-e zenering flows from the
b-e junction to either { mainly toward the collector }
or { about equally toward the collector and the other
way }, depending on the package type. That heat will
flow thru thermal resistance, leading to a temperature
difference between the b-e junction and the regions
where the temperature effect mainly occurs. I imagine
you could hold the b-e junction temperature constant,
but that would mean the regions where the temperature
effect occurs would not be constant.

If you are claiming the temperature drop between the
b-e junction and { the base region and c-b junction }
is too small to justify worry about its variation, then I
can only say that depends on the magnitude of the
temperature effect relative to the sum of the others.
I don't know how to avoid the worry based on what
is known about that.

With the AC excitation at a suitable frequency, both
the capacitance effect (due to junction voltages not
being constant) and the thermal effect have a fortunate
phase relationship to the "bez" effect, which has no
way to be slow enough to be anything but in phase
with the excitation.

The capacitances interacting with each other form capacitive
voltage dividers. The E-B junction has a low and real impedance when it
is zenered. This makes a path for the capacitance to carry an in phase AC
component to the collector lead.

I cannot see that. The b-e capacitance and the b-e voltage
change required to modify the tunnelling probability (as real
an impedance as can be) are in parallel. If the base is AC
grounded, the current from those two components of the
emitter admittance can be separated as the in phase and
quadrature phase components.

Here is what I think the setup will look like:
___
.------|___|------.
| |
| * || |
o-------------||--o
| || |
| |\| |
o--------|-\ |
| | >-----'
| +3V-|+/
GND DUT | |/|
DC source | |/
/ \ GND-|
( ~ ) |> * = HF stabilization only
\_/ |
GND | ___ |
| '----|___|---o
/ \ |
( ~ ) ---
\_/ Sig gen ---
| ___ |
'----------|___|---'

Constructive comments are welcome.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[John Woodgate]

I read in sci.electronics.design that John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote (in
<6om041l8dc13lricne6bcqj0i3k45lhbqi@4ax.com&gt about 'an electronish
puzzle', on Tue, 22 Mar 2005:

I'd like to plop a single 0603 NTC cap on the board to do the same
thing,

I suggest you go to all the ceramic cap makers you can find and plead
for a few (thousand?) parts from ANY reasonable-valued run of NTC that
they happen to be doing (or have as unallocated stock).
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[John Larkin]

On Fri, 25 Mar 2005 09:13:28 -0800, "Larry Brasfield"
<donotspam_larry_brasfield@hotmail.com> wrote:

"Ken Smith" <kensmith@green.rahul.net> wrote in
message news:d201na$ag6$2@blue.rahul.net...
In article <7mD0e.20$TJ1.579@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:
"Ken Smith" <kensmith@green.rahul.net> wrote in
message news:d1ultn$8gp$1@blue.rahul.net...
...
1nA * 1mS = 1pC

Charging the junction capacitances is going to cause a current spike that
may be bigger than the value to be measured. This makes for some
instumentation problems.

Quite so. I plan to use single frequency excitation. That makes
extraction of signal from noisy sample data a little easier too.

How are you going to deal with the non-linearities of the capacitances and
the fact that they don't have a zero damping factor?

Can you elaborate on that? (maybe after considering
the discussion on non-linearity as developed below)
The "damping factor" issue completely escapes me.

Using a single
frequency seems like a bad idea because it allows confounding variables
into the issue.

It seems to me that it allows better separation of the
confounding variables, at least the ones I know of.
Which variables do you believe are more confounding
with single frequency excitation? (Mind you, I am
not saying only one frequency is to be used in the
experiment -- just that they are used one at a time.)

The fact that the capcitances are not linear
makes life even more interesting.

Well, they are nonlinear, but the voltages across
both junctions are or can be held pretty constant.
(I plan to use a conventional, low Z-in photoamp
circuit to collect the collector output current.)

What will happen to the capacitance of the E-B juntion as the zener
current changes?

I don't think it is sensitive to current per-se. To get
that current change, the voltage must change. And
that modulates the depletion region width, which of
course is as non-linear as the doping profile is non-
constant (away from the junction itself).

I agree that non-linearity can be a real complication.
But its impact can be reduced by using the AC
excitation approach, with signals made small enough.

...
Figure out some way to make an electric heater keep the junction
temperature constant. The semiconductor to case resistance is a linear
effect. The effective location of the heat source within that
semiconductor may move a little when the current changes, but I think that
that is going to be too small of an effect to worry about.

If I read that correctly, you mean to permit a DC
measurement of the b-e zenering effect, separated
from the temperature effect, by holding some
temperature within the device constant under DC
conditions. (If it was transient or AC conditions,
the cure would be harder than the problem.)

One problem with that approach is that there are
temperature gradients within the device when you
dissipate power at/around/in a junction, but the
"bez" effects are not necessarily occuring at the
same places as the dissipation. For example,
the temperature effect on c-b leakage itself
occurs throughout the base region and in the
c-b depletion region. You would need to hold
those temperatures constant.

I'll remind you that I said:
[cite cut]
temperature constant. The semiconductor to case resistance is a linear
effect. The effective location of the heat source within that
semiconductor may move a little when the current changes, but I think that
that is going to be too small of an effect to worry about.

I still think this is true.

I think so too. I did not mean to contravene that,
but to bring up a larger difficulty with trying to hold
some relevant temperature constant. I will try to
state the point less obliquely.

The heat generated by the b-e zenering flows from the
b-e junction to either { mainly toward the collector }
or { about equally toward the collector and the other
way }, depending on the package type. That heat will
flow thru thermal resistance, leading to a temperature
difference between the b-e junction and the regions
where the temperature effect mainly occurs. I imagine
you could hold the b-e junction temperature constant,
but that would mean the regions where the temperature
effect occurs would not be constant.

If you are claiming the temperature drop between the
b-e junction and { the base region and c-b junction }
is too small to justify worry about its variation, then I
can only say that depends on the magnitude of the
temperature effect relative to the sum of the others.
I don't know how to avoid the worry based on what
is known about that.

With the AC excitation at a suitable frequency, both
the capacitance effect (due to junction voltages not
being constant) and the thermal effect have a fortunate
phase relationship to the "bez" effect, which has no
way to be slow enough to be anything but in phase
with the excitation.

The capacitances interacting with each other form capacitive
voltage dividers. The E-B junction has a low and real impedance when it
is zenered. This makes a path for the capacitance to carry an in phase AC
component to the collector lead.

I cannot see that. The b-e capacitance and the b-e voltage
change required to modify the tunnelling probability (as real
an impedance as can be) are in parallel. If the base is AC
grounded, the current from those two components of the
emitter admittance can be separated as the in phase and
quadrature phase components.

Here is what I think the setup will look like:
___
.------|___|------.
| |
| * || |
o-------------||--o
| || |
| |\| |
o--------|-\ |
| | >-----'
| +3V-|+/
GND DUT | |/|
DC source | |/
/ \ GND-|
( ~ ) |> * = HF stabilization only
\_/ |
GND | ___ |
| '----|___|---o
/ \ |
( ~ ) ---
\_/ Sig gen ---
| ___ |
'----------|___|---'

Constructive comments are welcome.

Are you going to measure it, or talk it to death? I could have done it
in 10 minutes, about twice what it took to do the DC version.

John

 

[Fred Bloggs]

John Larkin wrote:

On Tue, 22 Mar 2005 09:13:25 -0600, John Fields
jfields@austininstruments.com> wrote:


On Mon, 21 Mar 2005 16:24:58 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:


On Mon, 21 Mar 2005 15:39:06 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:



You wrote earlier:
It's apparently linear up to Ie of 10 mA, all i did,
at which time Ic is up to 260 nA.
If it was not exponential, as the temperature effect
would cause, then either your transistor is going
into avalanche or the mechanism at work is one
which has eluded everybody here (who played),
including myself, along with a number of bright
interviewees including one with a PhD obtained
after his work in novel semiconductor devices.
I will soon be asking him again about this puzzle.
For all I know, there could be another, parallel
effect in addition to all the tunneling.



I'm an engineer, so when theory collides with parts, I trust the
parts.


"One experiment is worth a thousand expert opinions."

- Werner Von Braun.


---
Fred Bloggs wrote:

In the case of the OP292 thread, the motivation was to make a dead
certain diagnosis of the Nazi Clarence and his problem- and that is
what I did- also ordered some OP292's and played around with it some
more.
...


John Larkin wrote:

You actually ordered parts and built circuits to prove somebody from a
newsgroup to be wrong? That's pushing the top range of the
getalifeometer!

...


If you believe what you quoted:, "One experiment is worth a thousand
expert opinions.", then buying or building parts to prove a point in
the real world isn't something which should be ridiculed, it's
something which should be respected. After all, spending
discretionary income just to prove a point with no hope of
remuneration or, God forbid, gain, rocks. That is, it proves
committment to an ideal.



The "ideal", in his case, is to prove other people stupid in cases
where ordinary insults and obscenities aren't enough.

That's your take on it- but then everyone knows you are smug narcissist
who isn't nearly as smart, creative , and fun as you think you are.
There is no great effort to prove Clarence is stupid- that is
immediately apparent from his posts- a lot brain damage/defect and
ignorance.

If Fred had a legitimate need, or just intellectual curiosity, about
this issue, then that has my respect; so why doesn't he share it with
us?

There is more of your narcissism- like who cares what you do or do not
respect. And I don't know why you would have any respect for me- I
certainly have none for you- this should be clear to you by now- what's
there about you to respect or even be interested in.