Someone deserves an IgNobel prize for inventing them.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
tly. Between
ration
p properly.
s John suggested. Those things are slabs of misery, for sure.
hose things, but having bad layout strays is one of the ways to not build w hat you think you're building.
r? Otherwise it's possible the op amp is counterfeit.
ll free-men-and-equals round here.)
Sorry Phil...Still in grad school, so I'm just used to saying "Dr." if I do n't know the person and I see those letters near their name.
As for all the other replies including your own:
The pnp C-multiplier guy was drawn wrong. Drew it last night. I know it was as we measured both +/-10V with a DMM and with a scope to check for oscill ations.
The whole circuit was built on piece of copper clad board. Made the job tig ht. Lifting input pins of the op amps off of the copper clad board. Used 06
03 caps and resistors and 30AWG for connections. I will tell my co-worker t o add another C-multiplier for the photodiode and to add some beefy caps on the supply pins. And to consider using single package opamps instead of du al package.Both of us (my co-worker and I) have Phil's book and AoE. Read through a li ttle bit of each book (Ch 14 and 18 of Phil's and Ch 88 of AoE 3rd ed) plus a couple of papers of Phil's. Did the initial calculations for our design (I haven't really prototyped my balance PD yet) to ensure shot noise limite d. and for the most part it works. The TIA worked nicely. It wasn't until h e added the non-inverting amplifier did the BW decrease. Eventually, he swi tched to the inverting configuration and the BW issue disappeared and the n oise results were satisfactory for the physicist that we're both doing our prototypes for.
As for his specs: 50nW of light, PD: PC5-6-TO5, BW = 50kHz, light wavelen gth = 852nm
ectly. Between
guration
up properly.
as John suggested. Those things are slabs of misery, for sure.
those things, but having bad layout strays is one of the ways to not build what you think you're building.
tor? Otherwise it's possible the op amp is counterfeit.
all free-men-and-equals round here.)
don't know the person and I see those letters near their name.
as as we measured both +/-10V with a DMM and with a scope to check for osci llations.
ight. Lifting input pins of the op amps off of the copper clad board. Used
0603 caps and resistors and 30AWG for connections. I will tell my co-worker to add another C-multiplier for the photodiode and to add some beefy caps on the supply pins. And to consider using single package opamps instead of dual package.little bit of each book (Ch 14 and 18 of Phil's and Ch 88 of AoE 3rd ed) pl us a couple of papers of Phil's. Did the initial calculations for our desig n (I haven't really prototyped my balance PD yet) to ensure shot noise limi ted. and for the most part it works. The TIA worked nicely. It wasn't until he added the non-inverting amplifier did the BW decrease. Eventually, he s witched to the inverting configuration and the BW issue disappeared and the noise results were satisfactory for the physicist that we're both doing ou r prototypes for.
ength = 852nm
Sorry....Ch8 of AoE, not Ch 88
They work okay for making a PIC blink a LED, as long as they're new.
Then of course somebody plugs in a resistor from an old reel without removing the residual adhesive, and two of the holes become flaky forever. Then the next resistor is maybe oversize, and bends the crappy metal fingers apart, and the one after that is corroded, and leaves semi-insulating dust all over the place....
Not to mention a couple of pF of capacitance between adjacent rows, and many nanohenries in series with all the (nastily daisy chained) grounds.
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
15 meg feedback, into the opamp+photodiode capacitance, is kind of scary. Huge noise peaking, or oscillation, might happen.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Okay, good.
As a SWAG, I'd say it's still getting in via the negative supply. As John says, the fact that inverting the output polarity (and hence the current required to drive the cable) changes the bandwidth is pretty diagnostic.
At 50 kHz, a 6-foot cable (200 pF) will be pulling
i_out = 2 pi * 50kHz * 200pF = 63 uA per volt of output amplitude, with a 90-degree phase lead.
That volt of output is 1V/45M = 22 nA. To get 22 nA through 10 pF at 50 kHz requires a supply jiggle of
v_ripple = 22nA/(2 pi * 50kHz * 10e-12) = 7 mV.
That's a very believable number for a lightly loaded cap multiplier. Using a separate one for the PD, and loading it down so that it 's drawing a few milliamps ought to fix it. A 2k resistor from each supply pin to ground will stiffen the supplies a lot.
Meanwhile, try measuring the output with a x10 probe!
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
Grin, I was laying out this little pressure circuit for testing the other day, a few flaky connections later and I grabbed my soldering iron and copper clad.
I need to order more (copper clad) any decent sources?
George H.
It's super cheap on eBay.
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
ebay usually has tons. Or I can send you a few sheets. I might even include a bit of the gold stuff.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Hey Phil...Just to clarify, you're suggesting a 2kohm resistor to gnd on all c-multiplier outputs (3 of them: +/- 10V for the opamps and -10V for the PD), right? we'll try using a x10 scope probe for the non-inverting configuration.
correctly. Between
onfiguration
ired up properly.
ard, as John suggested. Those things are slabs of misery, for sure.
py
ds.
r day,
clad.
op.JPG
Hey John...I'm always looking to improve my prototyping skills...What do yo u use to cut away your copper on your prototypes? I just use a razor and sl ice back and forth, but then I may create shorts when I fill that part with solder. I see your prototypes have a pretty good clearance when cutting aw ay the copper to make isolated pads.
Serrated aviation snips (Wiss M3). They last for years.
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
Yup. The output impedance of the cap multipliers is 25 ohms / I(mA).
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
For making pads, you cut up small rectangles and glue them to the ground plane. That makes good power supply bus bars, too.
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
No worries I ordered some from Mouser. (yeah perhaps over paid.)
George H.
56_Top.JPG
That is true and I'll glue my surfboards onto the copper boards for ICs (wh en required), but I noticed John cut away his copper in a pretty nice fashi on (along with gluing boards). As for me, I prefer to cut away copper for i solated pads instead of gluing a bunch of small pieces of copper to the boa rd. Mainly because I never have glue around when I need it. And those serra ted aviation clips. We have them and I hate them :) I can't cut straight lo ng (several inches) pieces of copper board to save my life. Which is why I bought a cheap-o mighty mite table saw from harbor freight. But since I hav e to make a purchase for some lab supplies, I'll just buy a bulk of glue an d be done with it.
Z356_Top.JPG
t dwhen required), but I noticed John cut away his copper in a pretty nice fas hion (along with gluing boards). As for me, I prefer to cut away copper for isolated pads instead of gluing a bunch of small pieces of copper to the b oard. Mainly because I never have glue around when I need it. And those ser rated aviation clips. We have them and I hate them :) I can't cut straight long (several inches) pieces of copper board to save my life. Which is why I bought a cheap-o mighty mite table saw from harbor freight. But since I h ave to make a purchase for some lab supplies, I'll just buy a bulk of glue and be done with it.
paper guillotines work quite well for copper clad
for islands I use a box cutter or scalpel
-Lasse
Lately I use a Dremel with a carbide dental burr. It takes a bit of practice. Finish off with x-acto trim and a healthy rub with Scotchbrite.
You can also mount parts on insulated pedestals of FR4. I use krazy glue, recommeded by Dr Phil.
Sadly, the beautiful copper prototypes get grungy in a few weeks. That's why I had some FR4 gold plated.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Felipe Jimenez prodded the keyboard with:
A really cheap circular saw to cut up FR4 and similar PCB material is
needed. A bargin at twice the price.
--
Best Regards:
Baron.
We have an ancient rusty hand shear/brake thing that I use to cut FR4. We also have a nice shiny foot shear, but I'm not allowed to use it. The epoxy-glass dulls the blades.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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