On 2008-11-05, CBFalconer <cbfalconer@yahoo.com> wrote:
> Andrew Smallshaw wrote:
>> Oliver Betz <obetz@despammed.com> wrote:
>> 
>>> My calc above should demonstrate that 1pA is 6 million electrons
>>> per second. Hard to measure this "current" with 100MHz bandwith.
>> 
>> In isolation, that's actually quite doable.  Electron multipliers
>> can easily detect individual electrons.  I've used them in the past
>> in the form of photomultipliers.  100MHz is quite fast but ISTR
>> seeing PMTs with quoted sub-nanosecond response times.  If PMTs
>> can work at those kind of speeds then plain electron multipliers
>> must also be able to work at those speeds.
>
> FYI we have been detecting single electrons with photo-multipliers
> for at least the past 60 years.  I can personally vouch for about
> 55 of them.
>
> I fail to see how you can describe the action of a single electron
> in terms of frequency.  I consider that a frequency requires a
> wave, which in turn requires a large multiplicity of point-style
> objects to simulate.

I wasn't referring to the frequency of an electron, wave/particle
duality or any other area of theoretical physics, but to the the
mechanics of actually counting the electrons and recording when
they arrive.  The current from a PMT isn't sharply defined - it
has a definite rise and fall time just like anything else.  While
the tube itself is asynchronous in operation the same is probably
not true of the surrounding circuitry.  To keep that circuitry
simple you want to interpret the PMT output as a simple binary
signal - is there a photon/electron there or not - and the response
time of the tube should be short compared to the sampling frequency
to reduce the effects of what happens when an individual pulse
straddles a clock transition.

-- 
Andrew Smallshaw
andrews@sdf.lonestar.org

In article <49122965.B3C039CB@yahoo.com>, cbfalconer@yahoo.com says...
> Andrew Smallshaw wrote:
> > Oliver Betz <obetz@despammed.com> wrote:
> > 
> >> My calc above should demonstrate that 1pA is 6 million electrons
> >> per second. Hard to measure this "current" with 100MHz bandwith.
> > 
> > In isolation, that's actually quite doable.  Electron multipliers
> > can easily detect individual electrons.  I've used them in the past
> > in the form of photomultipliers.  100MHz is quite fast but ISTR
> > seeing PMTs with quoted sub-nanosecond response times.  If PMTs
> > can work at those kind of speeds then plain electron multipliers
> > must also be able to work at those speeds.
> 
> FYI we have been detecting single electrons with photo-multipliers
> for at least the past 60 years.  I can personally vouch for about
> 55 of them.
> 
> I fail to see how you can describe the action of a single electron
> in terms of frequency.  I consider that a frequency requires a
> wave, which in turn requires a large multiplicity of point-style
> objects to simulate.

To be pedantic some form of repetitive occurance, even signalling
with lights using Morse Code has 'burst frequency', but the code
patterns are not exactly waves in themselves. The light is 
(depending on whether you view the photons at that time as a
wave or a particle....).


-- 
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<http://www.pcserviceselectronics.co.uk/>    PC Services
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Andrew Smallshaw wrote:
> Oliver Betz <obetz@despammed.com> wrote:
> 
>> My calc above should demonstrate that 1pA is 6 million electrons
>> per second. Hard to measure this "current" with 100MHz bandwith.
> 
> In isolation, that's actually quite doable.  Electron multipliers
> can easily detect individual electrons.  I've used them in the past
> in the form of photomultipliers.  100MHz is quite fast but ISTR
> seeing PMTs with quoted sub-nanosecond response times.  If PMTs
> can work at those kind of speeds then plain electron multipliers
> must also be able to work at those speeds.

FYI we have been detecting single electrons with photo-multipliers
for at least the past 60 years.  I can personally vouch for about
55 of them.

I fail to see how you can describe the action of a single electron
in terms of frequency.  I consider that a frequency requires a
wave, which in turn requires a large multiplicity of point-style
objects to simulate.

-- 
 [mail]: Chuck F (cbfalconer at maineline dot net) 
 [page]: <http://cbfalconer.home.att.net>
            Try the download section.

On 2008-11-05, Oliver Betz <obetz@despammed.com> wrote:
>
> My calc above should demonstrate that 1pA is 6 million electrons per
> second. Hard to measure this "current" with 100MHz bandwith.

In isolation, that's actually quite doable.  Electron multipliers
can easily detect individual electrons.  I've used them in the past
in the form of photomultipliers.  100MHz is quite fast but ISTR
seeing PMTs with quoted sub-nanosecond response times.  If PMTs
can work at those kind of speeds then plain electron multipliers
must also be able to work at those speeds.

Whilst that's all very interesting I can't see how to use it in
the intended application.  For an electron multiplier to work you
need the electrons to be both fairly energetic and in free space
- it isn't the the kind of thing you connect up with wires.  I
don't think either of those parameters will be easily satisfied in
the OP's app.

-- 
Andrew Smallshaw
andrews@sdf.lonestar.org

On 2008-11-05, linnix <me@linnix.info-for.us> wrote:
>
> Yes, you are right.  One electron is E-19 Amp, or E19 electrons to get
> one Amp one Volt.  I am trying to tell the OP that the odd is E19
> against him.

Oh dear.  One electron is 1.6E-19 COULOMBS.  One electron _per_second_
gives you 1.6E-19 amps.  None of which tells you anything about
the voltage.

-- 
Andrew Smallshaw
andrews@sdf.lonestar.org

On Nov 5, 5:05 am, Oliver Betz <ob...@despammed.com> wrote:
> linnix wrote:
>
> [...]
>
> >> >100 MHz bandwidth in pA range (precision is TBD, I assume something
> >> >modest like 8 bits) is dreamland given your level of expertise as you
> >> >describe it.
> >> >It is probably dreamland for anyones level of expertise today, for
> >> >that,
> >> >(but I am not sure - I have not looked deeply into it).
>
> >> 1pA / e = 6E10/s
>
> The correct value is 6E6/s, or 6 million electrons per second.
>
> >And 1 eV is 1.6E-19 V
>
> maybe I missed the joke, but that's wrong. eV is an enery unit, 1eV is
> 1.6E-19J.
>
> My calc above should demonstrate that 1pA is 6 million electrons per
> second. Hard to measure this "current" with 100MHz bandwith.
>

Yes, you are right.  One electron is E-19 Amp, or E19 electrons to get
one Amp one Volt.  I am trying to tell the OP that the odd is E19
against him.

> Oliver
> --
> Oliver Betz, Munich
> despammed.com might be broken, use Reply-To:

linnix wrote:

[...]

>> >100 MHz bandwidth in pA range (precision is TBD, I assume something
>> >modest like 8 bits) is dreamland given your level of expertise as you
>> >describe it.
>> >It is probably dreamland for anyones level of expertise today, for
>> >that,
>> >(but I am not sure - I have not looked deeply into it).
>>
>> 1pA / e = 6E10/s

The correct value is 6E6/s, or 6 million electrons per second.

>And 1 eV is 1.6E-19 V

maybe I missed the joke, but that's wrong. eV is an enery unit, 1eV is
1.6E-19J.

My calc above should demonstrate that 1pA is 6 million electrons per
second. Hard to measure this "current" with 100MHz bandwith.

Oliver
-- 
Oliver Betz, Munich
despammed.com might be broken, use Reply-To:

On Mon, 03 Nov 2008 12:27:02 -0600, mitakeet wrote:

> As I mentioned, I have no clue how practical even detecting the change
> in current is.  I will have a 10 nm or so channel (3-5 nm deep) with a
> fluid that is mostly water with some number of charged molecules flowing
> through it.  The charged molecules will be around 1 nm in diameter.  My
> goal is to detect the change in current flow between two conductors that
> are broken by the channel.  

OK, so it probably is about DNA sequencing. This is not a novel idea,
there are people working on it for a couple of years. Why not ask them,
especially since they live near you?


-- 
		Przemek Klosowski, Ph.D. <przemek.klosowski at gmail>

On 3 Nov., 22:43, "mitakeet" <mitak...@sol-biotech.com> wrote:
> >You can easily find uC with 50 I/Os.  Two of them is far cheaper and
> >easier to deal with then FPGA.  Alternatively, a uC with a simple
> >CPLD.
>
> I thought that you could get FPGAs for not much more than twice that of a
> CPLD and that it was reasonable to get a 100 pin FPGA for $100 or less.
> Did I do a poor job of research or is $100 reasonable?

you can probably get a spartan3e with 100 user IOs for less than 10$

-Lasse

linnix wrote:
> 
... snip ...
> 
> And 1 eV is 1.6E-19 V.  Namely, a logic pin is activated by
> approximately E19 electrons. You will get the Nobel prize for
> measuring individual molecule or electron.
> An MBA getting the Nobel prize in physics will make history.

However, even an MBA will probably accept the 1.5e6 dollar prize.

-- 
 [mail]: Chuck F (cbfalconer at maineline dot net) 
 [page]: <http://cbfalconer.home.att.net>
            Try the download section.