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lock-in amplifier

Started by scot March 5, 2013
Marte Schwarz <marte.schwarz@gmx.de> writes:

> Hi John & Jim, > >>>>>> I seem to recall someone (John L?) talking about using opto-fets as zero >>>>>> charge injection switches. But I wonder are they really? They have fets >>>>>> inside, with gates that charge and discharge presumably. Hmm, not sure I >>>>>> understand how they work, now I come to think of it. Photovoltaic mode >>>>>> photodiode(s) connected to the gate I guess. > > Just think a little before flaming someone else, please.
Flaming? Really? First time I've been accused of that! It was an honest question. Just thinking aloud.
> opto-fets can never have a charge injection, because the charge they > use to load the gate comes from the chanel that the charge flows > in. so the sum will allways be zero. I would say, this is as obvious > as Kirchhoffs law can be.
Well, I don't think it is that obvious. Even Jim "charge is always conserved" Thompson doesn't seem to think so :) (And please, folks, we dont really need to go there again!) -- John Devereux
Hi John,

>> Just think a little before flaming someone else, please. > > Flaming? Really? First time I've been accused of that!
Well? You know how reliable Larkin's advice is >:-}
> It was an honest question. Just thinking aloud.
What a question?
>> opto-fets can never have a charge injection, because the charge they >> use to load the gate comes from the chanel that the charge flows >> in. so the sum will allways be zero. I would say, this is as obvious >> as Kirchhoffs law can be. > > Well, I don't think it is that obvious.
Where do you expect the injected charge comming from?
> Even Jim "charge is always conserved" Thompson doesn't seem to think so > :)
May be Jim woul tell his statement, too. I don't see any source for charge-injection. Marte
On Sat, 09 Mar 2013 21:38:57 +0100, Marte Schwarz
<marte.schwarz@gmx.de> wrote:

>Hi John, > >>> Just think a little before flaming someone else, please. >> >> Flaming? Really? First time I've been accused of that! > >Well? You know how reliable Larkin's advice is >:-} > >> It was an honest question. Just thinking aloud. > >What a question? > >>> opto-fets can never have a charge injection, because the charge they >>> use to load the gate comes from the chanel that the charge flows >>> in. so the sum will allways be zero. I would say, this is as obvious >>> as Kirchhoffs law can be. >> >> Well, I don't think it is that obvious. > >Where do you expect the injected charge comming from? > >> Even Jim "charge is always conserved" Thompson doesn't seem to think so >> :) > >May be Jim woul tell his statement, too. > >I don't see any source for charge-injection. > >Marte
How is a channel formed? There was no channel prior. Where did it come from? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On 3/9/2013 12:55 PM, Marte Schwarz wrote:
> Hi John & Jim, > >>>>>> I seem to recall someone (John L?) talking about using opto-fets >>>>>> as zero >>>>>> charge injection switches. But I wonder are they really? They have >>>>>> fets >>>>>> inside, with gates that charge and discharge presumably. Hmm, not >>>>>> sure I >>>>>> understand how they work, now I come to think of it. Photovoltaic >>>>>> mode >>>>>> photodiode(s) connected to the gate I guess. > > Just think a little before flaming someone else, please. > > opto-fets can never have a charge injection, because the charge they use > to load the gate comes from the chanel that the charge flows in. so the > sum will allways be zero. I would say, this is as obvious as Kirchhoffs > law can be. > > Regards > > Marte
The total photocurrent out of both leads has to be zero, averaged over an on-off cycle. (That's also true of a photodiode, of course.) But within an on-off cycle, you could have the gate charging current distributed in many possible ways. For instance, suppose it works like a MOSFET with a photovoltaic cell in its gate. Once the FET turns off, you'd expect the remaining gate charge to distribute itself in inverse proportion to the interelectrode capacitances. Of course if it's some clever structure, you could have all that charge recombine very rapidly, which would leave a lot less to couple via the capacitances. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
On Sat, 09 Mar 2013 15:59:59 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 3/9/2013 12:55 PM, Marte Schwarz wrote: >> Hi John & Jim, >> >>>>>>> I seem to recall someone (John L?) talking about using opto-fets >>>>>>> as zero >>>>>>> charge injection switches. But I wonder are they really? They have >>>>>>> fets >>>>>>> inside, with gates that charge and discharge presumably. Hmm, not >>>>>>> sure I >>>>>>> understand how they work, now I come to think of it. Photovoltaic >>>>>>> mode >>>>>>> photodiode(s) connected to the gate I guess. >> >> Just think a little before flaming someone else, please. >> >> opto-fets can never have a charge injection, because the charge they use >> to load the gate comes from the chanel that the charge flows in. so the >> sum will allways be zero. I would say, this is as obvious as Kirchhoffs >> law can be. >> >> Regards >> >> Marte > >The total photocurrent out of both leads has to be zero, averaged over >an on-off cycle. (That's also true of a photodiode, of course.) > >But within an on-off cycle, you could have the gate charging current >distributed in many possible ways. For instance, suppose it works like >a MOSFET with a photovoltaic cell in its gate. Once the FET turns off, >you'd expect the remaining gate charge to distribute itself in inverse >proportion to the interelectrode capacitances. > >Of course if it's some clever structure, you could have all that charge >recombine very rapidly, which would leave a lot less to couple via the >capacitances. > >Cheers > >Phil Hobbs
I'm just playing devil's advocate here, since I'm unsure myself. Until a photon hits, there is _no_ channel... assuming N-channel, there's two N+ plugs in a P-type substrate. How is the close-to-the surface P-type region changed to N-type upon application of photons? And where does the electron go? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Marte Schwarz <marte.schwarz@gmx.de> writes:

> Hi John, > >>> Just think a little before flaming someone else, please. >> >> Flaming? Really? First time I've been accused of that! > > Well? You know how reliable Larkin's advice is >:-}
>> It was an honest question. Just thinking aloud. > > What a question?
Well you snipped it didn't you?
>>> opto-fets can never have a charge injection, because the charge they >>> use to load the gate comes from the chanel that the charge flows >>> in. so the sum will allways be zero. I would say, this is as obvious >>> as Kirchhoffs law can be. >> >> Well, I don't think it is that obvious. > > Where do you expect the injected charge comming from?
The voltage at the gate changes, relative to the other terminals. There is a capacitance between the gate and the other terminals. dQ=C.dV.
>> Even Jim "charge is always conserved" Thompson doesn't seem to think so >> :) > > May be Jim woul tell his statement, too. > > I don't see any source for charge-injection.
The photodiode? (or whatever equivalent generates the change in gate voltage). -- John Devereux
On Sat, 09 Mar 2013 21:12:25 +0000, John Devereux
<john@devereux.me.uk> wrote:

>Marte Schwarz <marte.schwarz@gmx.de> writes: > >> Hi John, >> >>>> Just think a little before flaming someone else, please. >>> >>> Flaming? Really? First time I've been accused of that! >> >> Well? You know how reliable Larkin's advice is >:-} > >>> It was an honest question. Just thinking aloud. >> >> What a question? > >Well you snipped it didn't you? > >>>> opto-fets can never have a charge injection, because the charge they >>>> use to load the gate comes from the chanel that the charge flows >>>> in. so the sum will allways be zero. I would say, this is as obvious >>>> as Kirchhoffs law can be. >>> >>> Well, I don't think it is that obvious. >> >> Where do you expect the injected charge comming from? > >The voltage at the gate changes, relative to the other terminals. There >is a capacitance between the gate and the other terminals. dQ=C.dV. > >>> Even Jim "charge is always conserved" Thompson doesn't seem to think so >>> :) >> >> May be Jim woul tell his statement, too. >> >> I don't see any source for charge-injection. > >The photodiode? (or whatever equivalent generates the change in gate >voltage).
There is no gate in an opto-FET. Just a channel created by photon impacts... and maybe that's the secret sauce... CONTINUOUS photon impact is required to keep the FET on?? The pragmatist in me says, if opto-FET's were so wonderful, why am I not seeing them implemented as marvelous analog switches that are sweeping the world with their stupendous performance ?:-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On 3/9/2013 4:05 PM, Jim Thompson wrote:
> On Sat, 09 Mar 2013 15:59:59 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 3/9/2013 12:55 PM, Marte Schwarz wrote: >>> Hi John & Jim, >>> >>>>>>>> I seem to recall someone (John L?) talking about using opto-fets >>>>>>>> as zero >>>>>>>> charge injection switches. But I wonder are they really? They have >>>>>>>> fets >>>>>>>> inside, with gates that charge and discharge presumably. Hmm, not >>>>>>>> sure I >>>>>>>> understand how they work, now I come to think of it. Photovoltaic >>>>>>>> mode >>>>>>>> photodiode(s) connected to the gate I guess. >>> >>> Just think a little before flaming someone else, please. >>> >>> opto-fets can never have a charge injection, because the charge they use >>> to load the gate comes from the chanel that the charge flows in. so the >>> sum will allways be zero. I would say, this is as obvious as Kirchhoffs >>> law can be. >>> >>> Regards >>> >>> Marte >> >> The total photocurrent out of both leads has to be zero, averaged over >> an on-off cycle. (That's also true of a photodiode, of course.) >> >> But within an on-off cycle, you could have the gate charging current >> distributed in many possible ways. For instance, suppose it works like >> a MOSFET with a photovoltaic cell in its gate. Once the FET turns off, >> you'd expect the remaining gate charge to distribute itself in inverse >> proportion to the interelectrode capacitances. >> >> Of course if it's some clever structure, you could have all that charge >> recombine very rapidly, which would leave a lot less to couple via the >> capacitances. >> >> Cheers >> >> Phil Hobbs > > I'm just playing devil's advocate here, since I'm unsure myself. Until > a photon hits, there is _no_ channel... assuming N-channel, there's > two N+ plugs in a P-type substrate. How is the close-to-the surface > P-type region changed to N-type upon application of photons? And where > does the electron go? > > ...Jim Thompson >
For a switch, you don't care too much about that, I don't think, because a low-resistance channel will form pretty quickly. It's when the channel starts to disappear that injection becomes a problem, because it gets left on the hold capacitor to screw up your measurement. If all they are is a bog-standard photoconductor, i.e. a piece of nearly intrinsic Si with an ohmic contact on each end, the turn-off would happen by local recombination. (That would make sense given the 15-us speeds of those things.) Then the amount that gets kicked out the leads really would be near zero. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
On 3/9/2013 4:18 PM, Jim Thompson wrote:
> On Sat, 09 Mar 2013 21:12:25 +0000, John Devereux > <john@devereux.me.uk> wrote: > >> Marte Schwarz <marte.schwarz@gmx.de> writes: >> >>> Hi John, >>> >>>>> Just think a little before flaming someone else, please. >>>> >>>> Flaming? Really? First time I've been accused of that! >>> >>> Well? You know how reliable Larkin's advice is >:-} >> >>>> It was an honest question. Just thinking aloud. >>> >>> What a question? >> >> Well you snipped it didn't you? >> >>>>> opto-fets can never have a charge injection, because the charge they >>>>> use to load the gate comes from the chanel that the charge flows >>>>> in. so the sum will allways be zero. I would say, this is as obvious >>>>> as Kirchhoffs law can be. >>>> >>>> Well, I don't think it is that obvious. >>> >>> Where do you expect the injected charge comming from? >> >> The voltage at the gate changes, relative to the other terminals. There >> is a capacitance between the gate and the other terminals. dQ=C.dV. >> >>>> Even Jim "charge is always conserved" Thompson doesn't seem to think so >>>> :) >>> >>> May be Jim woul tell his statement, too. >>> >>> I don't see any source for charge-injection. >> >> The photodiode? (or whatever equivalent generates the change in gate >> voltage). > > There is no gate in an opto-FET. Just a channel created by photon > impacts... and maybe that's the secret sauce... CONTINUOUS photon > impact is required to keep the FET on?? > > The pragmatist in me says, if opto-FET's were so wonderful, why am I > not seeing them implemented as marvelous analog switches that are > sweeping the world with their stupendous performance ?:-) > > ...Jim Thompson >
Because they're 100 times too slow for general use, maybe. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
On Sat, 09 Mar 2013 16:29:09 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 3/9/2013 4:18 PM, Jim Thompson wrote: >> On Sat, 09 Mar 2013 21:12:25 +0000, John Devereux >> <john@devereux.me.uk> wrote: >> >>> Marte Schwarz <marte.schwarz@gmx.de> writes: >>> >>>> Hi John, >>>> >>>>>> Just think a little before flaming someone else, please. >>>>> >>>>> Flaming? Really? First time I've been accused of that! >>>> >>>> Well? You know how reliable Larkin's advice is >:-} >>> >>>>> It was an honest question. Just thinking aloud. >>>> >>>> What a question? >>> >>> Well you snipped it didn't you? >>> >>>>>> opto-fets can never have a charge injection, because the charge they >>>>>> use to load the gate comes from the chanel that the charge flows >>>>>> in. so the sum will allways be zero. I would say, this is as obvious >>>>>> as Kirchhoffs law can be. >>>>> >>>>> Well, I don't think it is that obvious. >>>> >>>> Where do you expect the injected charge comming from? >>> >>> The voltage at the gate changes, relative to the other terminals. There >>> is a capacitance between the gate and the other terminals. dQ=C.dV. >>> >>>>> Even Jim "charge is always conserved" Thompson doesn't seem to think so >>>>> :) >>>> >>>> May be Jim woul tell his statement, too. >>>> >>>> I don't see any source for charge-injection. >>> >>> The photodiode? (or whatever equivalent generates the change in gate >>> voltage). >> >> There is no gate in an opto-FET. Just a channel created by photon >> impacts... and maybe that's the secret sauce... CONTINUOUS photon >> impact is required to keep the FET on?? >> >> The pragmatist in me says, if opto-FET's were so wonderful, why am I >> not seeing them implemented as marvelous analog switches that are >> sweeping the world with their stupendous performance ?:-) >> >> ...Jim Thompson >> > >Because they're 100 times too slow for general use, maybe. > >Cheers > >Phil Hobbs
Maybe that's the answer... got to pile on a stream of photons before anything happens. Or too high an ON resistance? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.