1. Home
  2. Electronics Design
  3. Experiment
  4. Page 2

Experiment

d measurements in very low light (picoamps to nanoamps) and some reasonable bandwidth like 100 kHz to 1 MHz.

d round the output amp, and as I say, it's shot-noise limited above about 7 nA in a 1-MHz bandwidth (full scale is 1 uA). I could easily make a varian t that's quieter but slower (1 nA at the shot noise in 200 kHz, say), or wi th a bigger PD, or a lens to get more detection area. I might make those sp ecial-order options at first, like the fibre-coupled one.

You know much more about the PD market than I do. Are you going to have a variable gain? (different feedback R's) There is such a huge parameter sp ace for PD's. pA to mA, DC to "the moon" (GHz.) I have no idea where there is big demand .

Some configurable layout, with different options would be nice. I use one PCB for a few different PD's, different sizes, positions, R's and C's in the feedback path. Of course the options mean more traces and added capacitance where you don't want it.

George H.

Reply to
George Herold
Loading thread data ...

I'm leaning towards keeping the product super simple, so that I don't have to explain to people that all that noise on their scope is out of band (due to the omega C e_N effect). It's better just to filter it out and take a small bandwidth hit. The present circuit has about 35 parts in the actual TIA and another dozen or so in each of the two power supplies, and runs off an 18-V Meanwell wall wart or a random laptop brick. SPICE says it'll have way over 100 dB PSR (measured at the output), so it ought to be pretty trouble-free. Temperature compensating the PD leakage is an interesting problem--we'll see how big an effect it is in practice. (A few pA/K won't raise many eyebrows, but 1 nA/K would.)

Making it shot-noise limited at 1% of full scale gives it a pretty broad footprint in the parameter space, and its very reasonable price means that folks can just buy two different boxes if they need more range.

The fast vs slow, large vs small PDs, etc. are just component value changes on the same layout. Putting a Thor Labs half-inch threaded ring on the front would make it easier to use.

If it sells vaguely decently (like at least 25 units a year) we'd probably do some follow-ons such as noise cancellers, with an eye towards maybe getting into stabilized lasers and stuff like that eventually (but not till the effort is self-supporting).

If there's a lot of demand for much faster stuff at low current, I'll do one of those nice pHEMT/SiGe cascode things. The one I did 5 years or so ago got to within 6 dB of the shot noise of 1 nA in a 100-MHz bandwidth, but of course the input capacitance had to be super low, like

1 pF total. A few pHEMTs in parallel might get us up to the ~3 pF level while preserving that performance.

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 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

If you've got the time and the inclination, offering a few of those follow-ons up front proportionally increases your chance of a 'hit' with any given customer up front, too.

Many if not most businesses really get going selling something close to-- but other than--what they started off meaning to make.

Best of luck! James Arthur

Reply to
dagmargoodboat

Yeah, not a bad plan. The pHEMT one will take a bit of engineering, though. I might do the IBM thing and announce it for availability in 6 months, and see who bites. Those pHEMTs are stable enough that I might be able to parallel them directly--which would be pretty amazing for 20+ GHz devices (7 dB gain at 18 GHz).

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 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

d measurements in very low light (picoamps to nanoamps) and some reasonable bandwidth like 100 kHz to 1 MHz.

d round the output amp, and as I say, it's shot-noise limited above about 7 nA in a 1-MHz bandwidth (full scale is 1 uA). I could easily make a varian t that's quieter but slower (1 nA at the shot noise in 200 kHz, say), or wi th a bigger PD, or a lens to get more detection area. I might make those sp ecial-order options at first, like the fibre-coupled one.

Cambridge Instruments did "specials" which were costed as one-off adaptions .

The people who bought them tended to talk about them over coffee at confere nces, and some metamorphosed into regular products when other customers ask ed for them.

--
Bill Sloman, Sydney
Reply to
bill.sloman

That's sort of where I am with these ones--I've done similar things for various consulting customers, often for use in products. This way I can maybe get the OEM business. Recurring revenue is always comforting when you're a consultant. ;)

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 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.