lock-in amplifier

Mar 06, 2013 55 Replies
P

If they're just photoconductors, you have to build up enough photocarriers to get a decent ON resistance. To reduce the amount of light required, you want a long carrier lifetime (which is easy to get in silicon, of course) but then you have to wait for them to recombine.

Photoconductors also have twice full shot noise in the photocurrent portion--both the generation and recombination are stochastic. (The literature insists on making this somehow special by calling it 'GR noise' but the physics are pretty much the same as shot noise.

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
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J

Everyone has been calling them "FET's". Maybe they really are "photoconductors", some other semiconductor equivalent to CdS?? ...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.
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P

Dunno. Nobody else has used silicon photoconductors in yonks, so maybe Marketing decided to make it simpler for folks. Or maybe they work in a completely different way. (My money is on their being a silicon version of a Vactrol.)

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
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J

I wonder if Thompson is (still) smart enough to look at voltage:current curves and tell a resistor from a fet?

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John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
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J

so

CdS makes for nice audio AGC >:-} ...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.
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P

so

I think that photoconductors saturate like that too--there's a maximum accessible drift rate, and a finite supply of carriers. Polycrystalline CdS is a much crappier material.

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
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J

so

curves

Yep. Someone needs to tell Ol' Bird Brain that the only difference is the gate control. I still puzzle over why Larkin has to continue this asshole behavior. Will he ever grow up? ...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.
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P

they

obvious

There

so

curves

Please leave me out of the flame war. I'm interested in technical topics far more than in personalities.

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
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G

hey

ous

ere

.

nk so

        ...Jim Thompson
     ...Jim Thompson

Ahh, (a light dawns) you've mentioned the double shot noise in photoconductors, but I never got it.

I've got this 'weird' dark noise from the reverse biased LED's I've been playing with. I'm pretty sure it's after pulsing of the avalanche. Which they attribute to some sort of traps in the avalnche region. There's an observable 'bunchiness' in the counts.

George H.

(The

t -

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J

they

obvious

There

think so

curves

Same here. But Larkin just _will_not_ let it 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.
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R

they

obvious

There

think so

curves

Phil, you have my respect for that, unlike others who prefer to just fling dung (does it remind you of the chariot races at UBC?).

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B

they

s

vious

There

dV.

hink so

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n
I
        ...Jim Thompson

This shows up in SPADs - single photon avalanche diodes. The Milan mob have published useful stuff on that subject.

Bill Sloman, Sydney
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P

they

obvious

There

think so

curves

I never went to the chariot races. IIRC they were (a) an engineering thing, and (b) before my time. I heard about them from my big brother, who was in CS but hung out with a bunch of gears. They weren't the most welcoming crowd.

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
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R

they

obvious

There

think so

gate

curves

welcoming crowd.

Weird... I remember them and I'm pretty certain I was there after you. However, I also avoided the chariot race. Entering into a "race to the bottom" just didn't seem like a good idea.

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P

they

flows

obvious

There

dQ=C.dV.

think so

gate

I

recombine.

curves

welcoming crowd.

I graduated in '81. You?

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
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R

charge they

flows

obvious

There

dQ=C.dV.

think so

gate

I

get

recombine.

curves

welcoming crowd.

1988. EE.
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