niptechnology.com:
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be mile wide
my keyboard must be broken, it should have said "does not have to be mile w ide"
yep things DDR3 is supposed to be something like 40-50R
I have one a bit like that, but with a better base:
It does need a rubber band to apply a rotational preload to the arm.
I've often done that in high-Z TIAs, like 10M. The bootstrap effectiveness is limited by the capacitance to ground from the summing junction.
I wasn't expecting it to be a big issue with a 511-ohm TIA, but then I wasn't expecting that much capacitance either. I'll have to calculate whether the SAV-551+ can bootstrap the pour as well as the SiPM.
The usual local feedback tricks such as the PNP wraparound sort of need fast PNPs, which are no longer made. :( (The Renesas/Intersil ones are a sort-of exception.)
We're using this board as the front end to a time stretcher(*) for bathymetric lidar, which consists of an array of T/Hs sampling the same signal at ~300 ps intervals. The rep rate is only a kilohertz or thereabouts, so there's lots of time to digitize and read out the data.
A 14-bit, 3 GS/s digitizer would be a lot of iron to accomplish the same thing.
(*) _not_ a pulse stretcher.
Cheers
Phil Hobbs
"A sadder and a wiser man / he woke the morrow morn." (Coleridge)
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
I was think of a follower driving a follower, so the guard doesn't load the first one. Gain would be lower on the second bootstrap, but still a lot better than none.
-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Agreed, assuming the additional phase shift doesn't bite me in the backside. Might be a good application for a BFP650F.
I sometimes just bias a JFET bootstrap at its zero-TC current and use its output directly to drive the noninverting input of an op amp. You do get some residual DC offset, but in a high-Z TIA that's par for the course anyway, due to photodiode leakage current, so nobody minds.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
The SJ capacitance is 2.4 pF, as measured on a Boonton, about
Well, I took out the Dremel, with one of JL's fave dental burrs on it, and got the SJ capacitance down to 1.2 pF. It was actually pretty easy, and the results are sort of interesting-looking.
Top-to-bottom dimension is 18 mm.
Cheers
Phil Hobbs
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510
Is that a 2-layer board? They are usually about 15 pf per square inch, with a lot of fringing.
If we get our pcb laser blaster going, we'll mostly make 2-sided boards with all ground plane on the back. It will also be a huge time saver if we leave a lot of copper on the top, namely blast away just enough copper to make the insulated features. That will make a lot of capacitance, and lots of coplanar waveguide.
I'm envisioning secondary Dremel operations, or maybe a lot of lasering.
-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
No, it's 4 layers, with ground on L2. The #40 wire going down the middle of the canyon there replaces an L3 trace.
Fun. BTW PCBway recently cut their assembly prices by a lot.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
4layer boards come with free assemble from jlcpcb until xmas but they are limited to own their parts
Did you ever section that board? Maybe the L2 ground plane is very close to the layer 1 traces. Seems like a lot of c for some tiny features like that.
We got our own p+p line because kitting and logistics were a hassle for using outside assemblers.
-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
If I need to remove medium-size regions of copper, maybe up to 3/4 inch wide, from a prototype, then I peel it off as follows: Cut around the region I want to peel off, using a scalpel, saw, dremel or whatever. Then stick a knife, scalpel, etc under one corner to lift the copper off the epoxy just enough to grab hold of, then put a big hot metcal tip asross the line where I need the epoxy to peel off, e.g. SMTC-161, which softens the epoxy, and I grab the corner that I lifted with some good needle-nose pliers. Then I just pull gently upwards with the pliers as I slide the soldering iron so that it is always heating the part where it needs to peel off. Sometimes a little solder helps to get the heat from the iron into the copper foil. Peeling it this way is quick and doesn't create dust or copper swarf to get between pins etc.
I guess we could do that, around the capacitance-critical nodes.
-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Yeah, I cut one with snips and sanded it. The prepreg was a bit skinny, but not 0.1 mm. Mostly I got snookered by the AD8045 datasheet's specsmanship--their headline 1-GHz bandwidth number turns out to be a result of the details of the frequency compensation, and only applies in the noninverting configuration. Otherwise it's basically a pretty nice
600-MHz GBW op amp, but not something for sub-nanosecond work.The next version will connect the SAV-551+ bootstrap directly to the inverting input of an EL5166 CFA, and add a well-filtered chopamp to take out the resulting DC offset. The pHEMT's source won't even notice the current noise of the CFA, whereas if it were connected to the PD it would dominate the noise.
A nuisance, but quite a preventable one--my least favourite kind. :(
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Bootstrap into opamp inverting input? I don't understand that.
Do you know about THS4303? It's a roughly current-mode opamp with an internal g=+10 feedback network. 1.8 GHz net bw, and noise is pretty good.
-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
If you hang a pHEMT bootstrap on a photodiode, the gate and source go up and down together to decent accuracy.
The classical bootstrap architecture is off to the side, so that the TIA connects directly to the cathode of the PD. That makes the DC and low-frequency behaviour of the bootstrap device essentially irrelevant, which is nice. The down side is that the current noise of the TIA stage gets summed with the photocurrent, which can be a problem in low light.
Alternatively, though, you can connect the op amp to the source of the bootstrap device. There are op amps such as the LM6171A, which is basically a CFA with a follower driving its inverting input--this notion just uses the follower to bootstrap the PD as well as driving the inverting input. (Our QL01 nanowatt photoreceiver does that.)
Since the bootstrap's source follows its gate, this is pretty much equivalent except that (on the plus side) you can use much gnarlier op amps, and (on the minus side) the bootstrap has to have decent DC and low-frequency behaviour.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Why do people spoil such an interesting discussion by such excessive quoting? If one later searches the net for this discussion, one will drown in quotes...
-- Uwe Bonnes bon@elektron.ikp.physik.tu-darmstadt.de Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt --------- Tel. 06151 1623569 ------- Fax. 06151 1623305 ---------
There's this really useful button for that! It's labelled "PgDn"!
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
I still don't understand. If the bootstrap output drives the opamp, what is the input to the bootstrap?
Got a sketch?
-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Guess what: I know and use that button. But I don't understand to what purpose people force me to use it multiple times.
Bye
-- Uwe Bonnes bon@elektron.ikp.physik.tu-darmstadt.de Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt --------- Tel. 06151 1623569 ------- Fax. 06151 1623305 ---------
It's just duelling conveniences. Sitting on PgDn for a couple of seconds is a lot faster than snipping intelligently, so IMO it's okay to expect people to do that.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
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