Prev: Auditing Cases Interactive Learning Approach (4thEd) - Beasley – Instructors Solutions Manual in pdf format is available for purchase at affordable prices. Contact me at alltestbanks11[at]gmail.com to buy it today.
Next: Back Alley
From: Phil Hobbs on 23 Mar 2010 15:52
On 3/23/2010 3:47 PM, Paul Hovnanian P.E. wrote:
> Phil Hobbs wrote:
>>
>> On 3/23/2010 9:59 AM, George Herold wrote:
>>> On Mar 23, 8:32 am, Wimpie<wimabc...(a)tetech.nl> wrote:
>>>> On 23 mar, 12:57, Wimpie<wimabc...(a)tetech.nl> wrote:
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>> On 22 mar, 23:52, hal-use...(a)ip-64-139-1-69.sjc.megapath.net (Hal
>>>>
>>>>> Murray) wrote:
>>>>>> In article<4BA7797C.7020...(a)electrooptical.net>,
>>>>>> Phil Hobbs<pcdhSpamMeSensel...(a)electrooptical.net> writes:
>>>>
>>>>>>> Night lights use CdS or CdSSe photoconductors, but they don't have to
>>>>>>> have any kind of stability or repeatability, and they don't. (CdSSe's
>>>>>>> resistance can vary 5X due entirely to previous illumination history..)
>>>>
>>>>>> What is the mechanism for that history quirk?
>>>>
>>>>>> What is the time scale? How long does it remember the history?
>>>>
>>>>>> --
>>>>>> These are my opinions, not necessarily my employer's. I hate spam.
>>>>
>>>>> Hello,
>>>>
>>>>> Go towww.perkinelmer.comandsearch for "photocell", or follow the
>>>>> links. When at the photocell page, on the right side you have an
>>>>> application note link. They have a very nice document on the LDRs that
>>>>> includes the memory effect also.
>>>>
>>>>> Best regards,
>>>>
>>>>> Wim
>>>>> PA3DJSwww.tetech.nl
>>>>> without abc, PM will reach me
>>>>
>>>> The document that I have is no longer present on the Perkinelmer
>>>> website. Here:www.tetech.nl/divers/BRO_PhotoconductiveCellsAndAnalogOptoiso.pdf
>>>> you can find the document about LDR. I will leave it there for about
>>>> 10 days.
>>>>
>>>> Best regards,
>>>>
>>>> Wim
>>>> PA3DJSwww.tetech.nl- Hide quoted text -
>>>>
>>>> - Show quoted text -
>>>
>>> Thanks for the document, page 35 talks about shot noise in LDR's. Are
>>> they just throwing equations around or is there shot noise in LDR's?
>>>
>>> George H.
>>
>> The conductivity comes from photogenerated carriers, so there's one copy
>> of the shot noise there. Another copy comes from the stochastic
>> recombination, so a photoconductor with unity gain (i.e. where the
>> transit time equals the carrier lifetime) has exactly twice the shot
>> noise.
>>
>> If there's a lot of gain, i.e. you get to reuse the same carriers lots
>> of times before they recombine, the shot noise gets amplified too--just
>> like an APD or PMT.
>
>
> So, to paraphrase that: Shot noise is due to the carrier starting or
> stopping. The longer the device (greater transit time compared to
> recombination time) the more photons (or energy from an accelerating
> field as in a PMT) it takes to kick it the length of the soccer field
> (sorry about that analogy). But your current depends on the number of
> cariers that make it through the goal at the end.
>

Yes, except that the recombination time can be much longer than the
transit time--i.e. the same carriers can make the trip many times. Thus
you can have quite large photoconductive gains, as in CdS, where it can
be several thousand iirc.

There's a 1:1 tradeoff between gain and speed, because the current
builds up and dies away on the scale of the carrier lifetime rather than
the transit time. That's one reason CdS is so slow.

Cheers

Phil Hobbs

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
From: George Herold on 23 Mar 2010 15:59
On Mar 23, 2:58 pm, John Larkin
<jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> On Tue, 23 Mar 2010 10:39:15 -0700 (PDT), George Herold
>
>
>
>
>
> <ggher...(a)gmail.com> wrote:
> >On Mar 23, 11:33 am, John Larkin
> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> >> On Tue, 23 Mar 2010 06:59:08 -0700 (PDT), George Herold
>
> >> <ggher...(a)gmail.com> wrote:
> >> >On Mar 23, 8:32 am, Wimpie <wimabc...(a)tetech.nl> wrote:
> >> >> On 23 mar, 12:57, Wimpie <wimabc...(a)tetech.nl> wrote:
>
> >> >> > On 22 mar, 23:52, hal-use...(a)ip-64-139-1-69.sjc.megapath.net (Hal
>
> >> >> > Murray) wrote:
> >> >> > > In article <4BA7797C.7020...(a)electrooptical.net>,
> >> >> > >  Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> writes:
>
> >> >> > > >  Night lights use CdS or CdSSe photoconductors, but they don't have to
> >> >> > > >have any kind of stability or repeatability, and they don't.  (CdSSe's
> >> >> > > >resistance can vary 5X due entirely to previous illumination history.)
>
> >> >> > > What is the mechanism for that history quirk?
>
> >> >> > > What is the time scale?  How long does it remember the history?
>
> >> >> > > --
> >> >> > > These are my opinions, not necessarily my employer's.  I hate spam.
>
> >> >> > Hello,
>
> >> >> > Go towww.perkinelmer.comandsearchfor"photocell", or follow the
> >> >> > links. When at the photocell page, on the right side you have an
> >> >> > application note link. They have a very nice document on the LDRs that
> >> >> > includes the memory effect also.
>
> >> >> > Best regards,
>
> >> >> > Wim
> >> >> > PA3DJSwww.tetech.nl
> >> >> > without abc, PM will reach me
>
> >> >> The document that I have is no longer present on the Perkinelmer
> >> >> website. Here:www.tetech.nl/divers/BRO_PhotoconductiveCellsAndAnalogOptoiso.pdf
> >> >> you can find the document about LDR. I will leave it there for about
> >> >> 10 days.
>
> >> >> Best regards,
>
> >> >> Wim
> >> >> PA3DJSwww.tetech.nl-Hidequoted text -
>
> >> >> - Show quoted text -
>
> >> >Thanks for the document, page 35 talks about shot noise in LDR's.  Are
> >> >they just throwing equations around or is there shot noise in LDR's?
>
> >> >George H.
>
> >> Since photons make current, probably so. But LDRs are so messy it's
> >> likely buried in other gunk.
>
> >> One of my guys is building a test setup to measure shot/excess noise
> >> in resistors. We need a ~~ 100M resistor to create a small (50 nA
> >> maybe) bias current with below shot-level noise. It's not clear if
> >> high-value cermet resistors have shot noise or not, so we plan to
> >> measure a bunch.
>
> >> Metal film resistors don't go to very high values; we can probably get
> >> 10M and likely 22M, and maybe even 50M, so we may have to do a series
> >> string. Even then I want to measure them to make sure they behave. I'm
> >> guessing that axials are better than surface mount, because of the
> >> bigger available surface for depositing metal.
>
> >> It's an interesting problem, trying to generate a nA-range DC current
> >> with low noise. Low voltage across a low-value metal-film resistor
> >> doesn't work because of Johnson noise. High value resistors are noisy
> >> in their own right.
>
> >> John- Hide quoted text -
>
> >> - Show quoted text -
>
> >"> Since photons make current, probably so. But LDRs are so messy it's
> >> likely buried in other gunk."
>
> >Hmm, Yeah this is a bit confusing.  The photons make the charge
> >carriers and reduce the resistance... and as Phil H. says there is
> >generation and recombination noise.  But this should only depend on
> >the light level and not on how the device is biased.  For a given
> >light level if I double the bias voltage (and thus double the current)
> >does the noise go up?
>
> What's amazing to me is that there are resistors that *don't* have
> shot noise.
>
> Any time you have a current in which the electrons arrive randomly,
> there's shot noise. It's pure raindrops-on-the-roof statistics. That
> happens when the electrons are knocked loose by photons or when some
> thin barrier, like a P-N junction, doles out electrons across a
> surface. Metal wire is unique in having electron interactions that
> smooth out the flow. As far as I know, all semiconductor junction
> currents and leakages have shot noise. Tubes have shot noise.
>
> The shot noise current depends only on the average current; it goes up
> as the square root of I. Of course, some devices have more noise than
> pure shot noise.
>
>
>
> >I'm using 100M and 1 G resistors from Ohmite to make a 10nA current
> >source.  I'll look at the noise next chance I get.
>
> I'd appreciate that. We'll share whatever we learn. This is not very
> easy to measure.
>
> John- Hide quoted text -
>
> - Show quoted text -

"> I'd appreciate that. We'll share whatever we learn. This is not
very
> easy to measure."

Hmm I hadn't thought it would be that hard... but then I'm probably
missing something. I was going to take the the 10nA current source
and fed it into a TIA opamp circuit with 100Meg as feed back resistor,
(giving me a volt of DC across the resistor) And then see how noisy it
is. I can then compare it to 10 nA's from a photodiode.
Do you care about high frequencies (above 10kHz-100kHz or so..) or
very low frequencies? (There's 1/f noise in the FET opamp that starts
to interfere at the low end.)

Our noise apparatus is on a truck somewhere between here and Portland,
it may be back tomorrow though.

George H.
From: George Herold on 23 Mar 2010 16:06
On Mar 23, 3:20 pm, Phil Hobbs
<pcdhSpamMeSensel...(a)electrooptical.net> wrote:
> On 3/23/2010 2:58 PM, John Larkin wrote:
>
>
>
>
>
> > On Tue, 23 Mar 2010 10:39:15 -0700 (PDT), George Herold
> > <ggher...(a)gmail.com>  wrote:
>
> >> On Mar 23, 11:33 am, John Larkin
> >> <jjlar...(a)highNOTlandTHIStechnologyPART.com>  wrote:
> >>> On Tue, 23 Mar 2010 06:59:08 -0700 (PDT), George Herold
>
> >>> <ggher...(a)gmail.com>  wrote:
> >>>> On Mar 23, 8:32 am, Wimpie<wimabc...(a)tetech.nl>  wrote:
> >>>>> On 23 mar, 12:57, Wimpie<wimabc...(a)tetech.nl>  wrote:
>
> >>>>>> On 22 mar, 23:52, hal-use...(a)ip-64-139-1-69.sjc.megapath.net (Hal
>
> >>>>>> Murray) wrote:
> >>>>>>> In article<4BA7797C.7020...(a)electrooptical.net>,
> >>>>>>>   Phil Hobbs<pcdhSpamMeSensel...(a)electrooptical.net>  writes:
>
> >>>>>>>>   Night lights use CdS or CdSSe photoconductors, but they don't have to
> >>>>>>>> have any kind of stability or repeatability, and they don't.  (CdSSe's
> >>>>>>>> resistance can vary 5X due entirely to previous illumination history.)
>
> >>>>>>> What is the mechanism for that history quirk?
>
> >>>>>>> What is the time scale?  How long does it remember the history?
>
> >>>>>>> --
> >>>>>>> These are my opinions, not necessarily my employer's.  I hate spam.
>
> >>>>>> Hello,
>
> >>>>>> Go towww.perkinelmer.comandsearchfor"photocell", or follow the
> >>>>>> links. When at the photocell page, on the right side you have an
> >>>>>> application note link. They have a very nice document on the LDRs that
> >>>>>> includes the memory effect also.
>
> >>>>>> Best regards,
>
> >>>>>> Wim
> >>>>>> PA3DJSwww.tetech.nl
> >>>>>> without abc, PM will reach me
>
> >>>>> The document that I have is no longer present on the Perkinelmer
> >>>>> website. Here:www.tetech.nl/divers/BRO_PhotoconductiveCellsAndAnalogOptoiso.pdf
> >>>>> you can find the document about LDR. I will leave it there for about
> >>>>> 10 days.
>
> >>>>> Best regards,
>
> >>>>> Wim
> >>>>> PA3DJSwww.tetech.nl-Hidequoted text -
>
> >>>>> - Show quoted text -
>
> >>>> Thanks for the document, page 35 talks about shot noise in LDR's.  Are
> >>>> they just throwing equations around or is there shot noise in LDR's?
>
> >>>> George H.
>
> >>> Since photons make current, probably so. But LDRs are so messy it's
> >>> likely buried in other gunk.
>
> >>> One of my guys is building a test setup to measure shot/excess noise
> >>> in resistors. We need a ~~ 100M resistor to create a small (50 nA
> >>> maybe) bias current with below shot-level noise. It's not clear if
> >>> high-value cermet resistors have shot noise or not, so we plan to
> >>> measure a bunch.
>
> >>> Metal film resistors don't go to very high values; we can probably get
> >>> 10M and likely 22M, and maybe even 50M, so we may have to do a series
> >>> string. Even then I want to measure them to make sure they behave. I'm
> >>> guessing that axials are better than surface mount, because of the
> >>> bigger available surface for depositing metal.
>
> >>> It's an interesting problem, trying to generate a nA-range DC current
> >>> with low noise. Low voltage across a low-value metal-film resistor
> >>> doesn't work because of Johnson noise. High value resistors are noisy
> >>> in their own right.
>
> >>> John- Hide quoted text -
>
> >>> - Show quoted text -
>
> >> ">  Since photons make current, probably so. But LDRs are so messy it's
> >>> likely buried in other gunk."
>
> >> Hmm, Yeah this is a bit confusing.  The photons make the charge
> >> carriers and reduce the resistance... and as Phil H. says there is
> >> generation and recombination noise.  But this should only depend on
> >> the light level and not on how the device is biased.  For a given
> >> light level if I double the bias voltage (and thus double the current)
> >> does the noise go up?
>
> > What's amazing to me is that there are resistors that *don't* have
> > shot noise.
>
> > Any time you have a current in which the electrons arrive randomly,
> > there's shot noise. It's pure raindrops-on-the-roof statistics. That
> > happens when the electrons are knocked loose by photons or when some
> > thin barrier, like a P-N junction, doles out electrons across a
> > surface. Metal wire is unique in having electron interactions that
> > smooth out the flow. As far as I know, all semiconductor junction
> > currents and leakages have shot noise. Tubes have shot noise.
>
> > The shot noise current depends only on the average current; it goes up
> > as the square root of I. Of course, some devices have more noise than
> > pure shot noise.
>
> >> I'm using 100M and 1 G resistors from Ohmite to make a 10nA current
> >> source.  I'll look at the noise next chance I get.
>
> > I'd appreciate that. We'll share whatever we learn. This is not very
> > easy to measure.
>
> > John
>
> The electron arrival times are correlated by electron-electron
> scattering, which tends to smooth the flow out.    Rolf Landauer (a late
> IBM Fellow whom I knew very slightly) showed that the shot noise in a
> metal resistor is reduced by a factor of Ls/L, where L is the length of
> the element and L_s is the mean free path for electron-electron
> scattering.  In a typical device, that's 10 nm/1 mm, or 10**-5.
>
> Cheers
>
> Phil Hobbs
>
> --
> Dr Philip C D Hobbs
> Principal
> ElectroOptical Innovations
> 55 Orchard Rd
> Briarcliff Manor NY 10510
> 845-480-2058
> hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -
>
> - Show quoted text -

Yup that's the argument that I know. I had several discussions about
the lack of shot noise in resistors at the APS trade show. Someone
said there was no shot noise in resistors because it would violate the
Fluctuation-Dissipation Theorem. I don't know the F-D theorem well
enough to dissupute the statment.

George H.
From: John Larkin on 23 Mar 2010 16:16
On Tue, 23 Mar 2010 12:59:12 -0700 (PDT), George Herold
<ggherold(a)gmail.com> wrote:

>On Mar 23, 2:58�pm, John Larkin
><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>> On Tue, 23 Mar 2010 10:39:15 -0700 (PDT), George Herold
>>
>>
>>
>>
>>
>> <ggher...(a)gmail.com> wrote:
>> >On Mar 23, 11:33�am, John Larkin
>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
>> >> On Tue, 23 Mar 2010 06:59:08 -0700 (PDT), George Herold
>>
>> >> <ggher...(a)gmail.com> wrote:
>> >> >On Mar 23, 8:32�am, Wimpie <wimabc...(a)tetech.nl> wrote:
>> >> >> On 23 mar, 12:57, Wimpie <wimabc...(a)tetech.nl> wrote:
>>
>> >> >> > On 22 mar, 23:52, hal-use...(a)ip-64-139-1-69.sjc.megapath.net (Hal
>>
>> >> >> > Murray) wrote:
>> >> >> > > In article <4BA7797C.7020...(a)electrooptical.net>,
>> >> >> > > �Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> writes:
>>
>> >> >> > > > �Night lights use CdS or CdSSe photoconductors, but they don't have to
>> >> >> > > >have any kind of stability or repeatability, and they don't. �(CdSSe's
>> >> >> > > >resistance can vary 5X due entirely to previous illumination history.)
>>
>> >> >> > > What is the mechanism for that history quirk?
>>
>> >> >> > > What is the time scale? �How long does it remember the history?
>>
>> >> >> > > --
>> >> >> > > These are my opinions, not necessarily my employer's. �I hate spam.
>>
>> >> >> > Hello,
>>
>> >> >> > Go towww.perkinelmer.comandsearchfor"photocell", or follow the
>> >> >> > links. When at the photocell page, on the right side you have an
>> >> >> > application note link. They have a very nice document on the LDRs that
>> >> >> > includes the memory effect also.
>>
>> >> >> > Best regards,
>>
>> >> >> > Wim
>> >> >> > PA3DJSwww.tetech.nl
>> >> >> > without abc, PM will reach me
>>
>> >> >> The document that I have is no longer present on the Perkinelmer
>> >> >> website. Here:www.tetech.nl/divers/BRO_PhotoconductiveCellsAndAnalogOptoiso.pdf
>> >> >> you can find the document about LDR. I will leave it there for about
>> >> >> 10 days.
>>
>> >> >> Best regards,
>>
>> >> >> Wim
>> >> >> PA3DJSwww.tetech.nl-Hidequoted text -
>>
>> >> >> - Show quoted text -
>>
>> >> >Thanks for the document, page 35 talks about shot noise in LDR's. �Are
>> >> >they just throwing equations around or is there shot noise in LDR's?
>>
>> >> >George H.
>>
>> >> Since photons make current, probably so. But LDRs are so messy it's
>> >> likely buried in other gunk.
>>
>> >> One of my guys is building a test setup to measure shot/excess noise
>> >> in resistors. We need a ~~ 100M resistor to create a small (50 nA
>> >> maybe) bias current with below shot-level noise. It's not clear if
>> >> high-value cermet resistors have shot noise or not, so we plan to
>> >> measure a bunch.
>>
>> >> Metal film resistors don't go to very high values; we can probably get
>> >> 10M and likely 22M, and maybe even 50M, so we may have to do a series
>> >> string. Even then I want to measure them to make sure they behave. I'm
>> >> guessing that axials are better than surface mount, because of the
>> >> bigger available surface for depositing metal.
>>
>> >> It's an interesting problem, trying to generate a nA-range DC current
>> >> with low noise. Low voltage across a low-value metal-film resistor
>> >> doesn't work because of Johnson noise. High value resistors are noisy
>> >> in their own right.
>>
>> >> John- Hide quoted text -
>>
>> >> - Show quoted text -
>>
>> >"> Since photons make current, probably so. But LDRs are so messy it's
>> >> likely buried in other gunk."
>>
>> >Hmm, Yeah this is a bit confusing. �The photons make the charge
>> >carriers and reduce the resistance... and as Phil H. says there is
>> >generation and recombination noise. �But this should only depend on
>> >the light level and not on how the device is biased. �For a given
>> >light level if I double the bias voltage (and thus double the current)
>> >does the noise go up?
>>
>> What's amazing to me is that there are resistors that *don't* have
>> shot noise.
>>
>> Any time you have a current in which the electrons arrive randomly,
>> there's shot noise. It's pure raindrops-on-the-roof statistics. That
>> happens when the electrons are knocked loose by photons or when some
>> thin barrier, like a P-N junction, doles out electrons across a
>> surface. Metal wire is unique in having electron interactions that
>> smooth out the flow. As far as I know, all semiconductor junction
>> currents and leakages have shot noise. Tubes have shot noise.
>>
>> The shot noise current depends only on the average current; it goes up
>> as the square root of I. Of course, some devices have more noise than
>> pure shot noise.
>>
>>
>>
>> >I'm using 100M and 1 G resistors from Ohmite to make a 10nA current
>> >source. �I'll look at the noise next chance I get.
>>
>> I'd appreciate that. We'll share whatever we learn. This is not very
>> easy to measure.
>>
>> John- Hide quoted text -
>>
>> - Show quoted text -
>
>"> I'd appreciate that. We'll share whatever we learn. This is not
>very
>> easy to measure."
>
>Hmm I hadn't thought it would be that hard... but then I'm probably
>missing something. I was going to take the the 10nA current source
>and fed it into a TIA opamp circuit with 100Meg as feed back resistor,
>(giving me a volt of DC across the resistor) And then see how noisy it
>is.

Fine, as long as that 100M resistor has no excess noise of its own,
and you account for its Johnson noise, and the TIA has very little
input current noise. And all the supplies are very quiet. And
everything is really well shielded.

We're going to make a voltage divider from two identical RUTs, and AC
couple that into an opamp with a gain of +1000. The AC coupling RC
will add shunt Johnson noise but no excess noise of its own. We're
figuring on a polystyrene cap and a 1G resistor maybe. Opamp =
ADA4817. I figure we'd measure from 1 KHz to 100K maybe.

John

From: Robert Macy on 23 Mar 2010 16:20
On Mar 23, 11:26 am, George Herold <ggher...(a)gmail.com> wrote:
> On Mar 23, 1:42 pm, Robert Macy <m...(a)california.com> wrote:
>
>
>
>
>
> > On Mar 23, 10:39 am, George Herold <ggher...(a)gmail.com> wrote:
>
> > > On Mar 23, 11:33 am, John Larkin
>
> > > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> > > > On Tue, 23 Mar 2010 06:59:08 -0700 (PDT), George Herold
>
> > > > <ggher...(a)gmail.com> wrote:
> > > > >On Mar 23, 8:32 am, Wimpie <wimabc...(a)tetech.nl> wrote:
> > > > >> On 23 mar, 12:57, Wimpie <wimabc...(a)tetech.nl> wrote:
>
> > > > >> > On 22 mar, 23:52, hal-use...(a)ip-64-139-1-69.sjc.megapath.net (Hal
>
> > > > >> > Murray) wrote:
> > > > >> > > In article <4BA7797C.7020...(a)electrooptical.net>,
> > > > >> > >  Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> writes:
>
> > > > >> > > >  Night lights use CdS or CdSSe photoconductors, but they don't have to
> > > > >> > > >have any kind of stability or repeatability, and they don't..  (CdSSe's
> > > > >> > > >resistance can vary 5X due entirely to previous illumination history.)
>
> > > > >> > > What is the mechanism for that history quirk?
>
> > > > >> > > What is the time scale?  How long does it remember the history?
>
> > > > >> > > --
> > > > >> > > These are my opinions, not necessarily my employer's.  I hate spam.
>
> > > > >> > Hello,
>
> > > > >> > Go towww.perkinelmer.comandsearchfor"photocell", or follow the
> > > > >> > links. When at the photocell page, on the right side you have an
> > > > >> > application note link. They have a very nice document on the LDRs that
> > > > >> > includes the memory effect also.
>
> > > > >> > Best regards,
>
> > > > >> > Wim
> > > > >> > PA3DJSwww.tetech.nl
> > > > >> > without abc, PM will reach me
>
> > > > >> The document that I have is no longer present on the Perkinelmer
> > > > >> website. Here:www.tetech.nl/divers/BRO_PhotoconductiveCellsAndAnalogOptoiso.pdf
> > > > >> you can find the document about LDR. I will leave it there for about
> > > > >> 10 days.
>
> > > > >> Best regards,
>
> > > > >> Wim
> > > > >> PA3DJSwww.tetech.nl-Hidequotedtext-
>
> > > > >> - Show quoted text -
>
> > > > >Thanks for the document, page 35 talks about shot noise in LDR's.  Are
> > > > >they just throwing equations around or is there shot noise in LDR's?
>
> > > > >George H.
>
> > > > Since photons make current, probably so. But LDRs are so messy it's
> > > > likely buried in other gunk.
>
> > > > One of my guys is building a test setup to measure shot/excess noise
> > > > in resistors. We need a ~~ 100M resistor to create a small (50 nA
> > > > maybe) bias current with below shot-level noise. It's not clear if
> > > > high-value cermet resistors have shot noise or not, so we plan to
> > > > measure a bunch.
>
> > > > Metal film resistors don't go to very high values; we can probably get
> > > > 10M and likely 22M, and maybe even 50M, so we may have to do a series
> > > > string. Even then I want to measure them to make sure they behave. I'm
> > > > guessing that axials are better than surface mount, because of the
> > > > bigger available surface for depositing metal.
>
> > > > It's an interesting problem, trying to generate a nA-range DC current
> > > > with low noise. Low voltage across a low-value metal-film resistor
> > > > doesn't work because of Johnson noise. High value resistors are noisy
> > > > in their own right.
>
> > > > John- Hide quoted text -
>
> > > > - Show quoted text -
>
> > > "> Since photons make current, probably so. But LDRs are so messy it's
>
> > > > likely buried in other gunk."
>
> > > Hmm, Yeah this is a bit confusing.  The photons make the charge
> > > carriers and reduce the resistance... and as Phil H. says there is
> > > generation and recombination noise.  But this should only depend on
> > > the light level and not on how the device is biased.  For a given
> > > light level if I double the bias voltage (and thus double the current)
> > > does the noise go up?
>
> > > I'm using 100M and 1 G resistors from Ohmite to make a 10nA current
> > > source.  I'll look at the noise next chance I get.
>
> > > George H.
>
> > sorry for the VERY naive question, but would some form of junction
> > leakage have lower noise?  Or are junction leakages at and above
> > johnson?- Hide quoted text -
>
> > - Show quoted text -
>
> Not naive at all!  Phil is the expert here, but I'll answer anyway...
> (put my foot in mouth once again.)  So, as I understand it, the
> thermal (Johnson) noise from a biased junction is 1/2 of the thermal
> noise from a resistor that has the same resistance as the junction. (R
> = kT/(eV * I).  I beleive that Phil has actully used this 'trick' to
> make lower noise photodiode front ends... but it's a trick that is
> beyond my ability.
>
> George H.

Thank you for your reply.

Next naive question is Can the leakage be provided by a DC/DC
converter circuit where the supply's noise is caused by caps and
inductors, oh wait, no noise there. But I'm talking a physically
realizable circuit.
First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Prev: Auditing Cases Interactive Learning Approach (4thEd) - Beasley – Instructors Solutions Manual in pdf format is available for purchase at affordable prices. Contact me at alltestbanks11[at]gmail.com to buy it today.
Next: Back Alley