It doesn't make much difference, it turns out--if the plane is good enough for shielding, you get essentially the full capacitance.
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
Interesting. This board actually will be spending some significant fraction of its time being vibrated up and down at 100 Hz or so, so anything resembling a drum skin might be problematic.
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
Or just do it like the government folks, bootstrap the bootstrap that's already bootstrapped :-)
-- SCNR, Joerg http://www.analogconsultants.com/
Does the Megtron line fit?
I use Megtron 6 up to 204C/400F for downhole PCB work.
nd
ught
eThe low epsilon materials that I've actually used - both back around
1990 - were an essentially PTFE board filled with alumina to make it a bit stiffer and isocyanate-bonded PTFE cloth which we used as the two outer layers on a six-layer board, which was too floppy to be used on its own - the other three layers were FR4 epoxy-glass which made the board quite stiff enough for regular use, even though it was big - a triple-extended Eurocard.-- Bill Sloman, Sydney
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Ah, so you'll be even less interested in anything that looks like a banjo string--that's low leakage too, and could be strung across a sparse support structure. I'm not sure that's a gain over a bootstrapped line anyhow.
Depending on how crucial it is, how about John's kapton, but well- supported with a mechanical frame?
.---------------------------------|| |.-------. .-------. .-------..---|| || | | | | || ||.......'-'.......'-'.......||......
-----------------------------------
I'm not sure I understand. In order for the bootstrap to do its job, its gain has to be at least 0.997, and hopefully 0.999. The temperature and unit-to-unit stability issue is mostly with the capacitance in parallel with the feedback resistors. They're 1206 size, so routing a blind slot between the pads would be a good idea if the board house can do it. That would also solve the defluxing problem under there.
The total capacitance on the input node sets the high-frequency noise, but doesn't affect the frequency response much since the bootstrap's output impedance is only about an ohm.
The customer is pretty unlikely to go for anything too exotic in order to get another dB or so on top of the ~25 dB SNR improvement he's already getting with this front end. It might be different in the next version, where an extra few dB might help the marketing department.
I'd also worry about being able to stencil the solder paste cleanly if the board has too much surface relief.
Thanks
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
Thanks. From the plot on P 4 of the Megtron 4 datasheet, it looks like it's pretty leaky, so I wouldn't want to use it in such a high-Z application.
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
r y
The idea was to minimize capacitance using John's kapton film, but solve the mechanical vibration objections. You could air-wire it too, but that's both mechanically unstable and unbootstrappable, or at least that's what I was trying to acknowledge.
eYou're right, I was temp-compensating the bootstrap-to-signal- conductor capacitance. Nerrp.
The same concept(s) applies to the shunt C across the feedback resistor though--hang the feedback resistor in the air (bent-up IC leads work well for that), or provide a compensating printed-C element elsewhere in the bootstrap buffer artwork.
Sure, for big production. In that case you wouldn't want heroic labor- intensive measures, even if they offered an RCH's(*) improvement.
If the construction is stringing John's kapton conductor over Spehro's milled mesas, after soldering, that mightn't be so bad.
(*) A controversial, but standard engineering unit, learned from Jamie Ellot.
-- Cheers, James Arthur
Le Fri, 29 Mar 2013 10:08:39 -0400, Phil Hobbs a écrit:
Rogers Ro3003? Er = 3+/-0.04 +13ppm/K
-- Thanks, Fred.
Thanks. It sounds like nobody here has actually used any of these less-common Rogers materials, so I'll just have to throw myself on the mercy of the board house, I suppose. ;)
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
I've used Rogers RO3030 as a better FR4, with no problems. The dielectric constant is lower and more stable than FR4. No teflon knee. Otherwise, it processes just like FR4, and the same artwork was used. The characteristic impedance of the transmission lines did change, so some resistor values had to change.
Joe Gwinn
We did one board with layers of microwave laminate and FR4. It curled up like a potato chip.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Le Fri, 29 Mar 2013 10:08:39 -0400, Phil Hobbs a écrit:
I think there's a 10^6 coeff error (MOhm instead of Ohm). The bulk resistivity is given as 10^9MOhm.cm (about ten times the FR4 one) which, given a simplified 0.3mm/(0.3mmx0.75mm sample approximating the described test geometry) roughly tally with an initial 10^10MOhm.
Otherwise you have Rogers RO3003
Er = 3+/-0.04, +13ppm/K and 10^7 MOhm.cm
-- Thanks, Fred.
Le Fri, 29 Mar 2013 13:54:48 -0700, John Larkin a écrit:
RO3003 X and Y CTE are given at 16 & 17 ppm/K which is not too far from FR4 13 and 14 ppm/K.
We recently enquired for an odd 6 layers PCB (5 FR4 + 1 external RO6035HTC / CTE=19ppm/K) and the manufacturer (a pretty good one) didn't balk. Canceled though, so no board manufactured.
I think Phil's boards are pretty small, so warping if any should be benign.
-- Thanks, Fred.
I pulled a cruddy old piece of copperclad FR4 out of my junk box, cleaned the edges, and connected opposite sides to my Keithley electrometer. It's still charging up but it's over 1e16 ohm-cm and climbing.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Use any layer for slots, odd size holes, etc and call the gerber file .fab . I haven't come across a board house that didn't understand that. Having trenches instead of slots maybe be tougher because PCBs are usually drilled and routed in a stack.
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
That is one of the reasons i use Megtron 6 (used to use Megtron 5 but that is obsoleted by 6). But i though i should give you all the info i had for your evaluation. FYI, the Megtron line is derived from the original Geteck line courtesy of GE via Matushita.
Now it's 7e16 ohm-cm and still climbing, I think. The time constant seems to be days.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
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