It seems intuitive that a gap across copper will reduce current flow across the gap. This is true only at low frequencies. If you have any digital logic on this board, and there are any signal wires across the "gap", you've made an efficient transmitting / receive antenna. I think Joerg said if people didn't put gaps in their ground planes, he would have less work ;-) Sometimes the max current flows across the center of the gap. It's frequency selective.
Frank
Slot antennas and slotline transmission lines both suggest modes better left alone.
John
I have pointed you to that before so it is not that you have yet to see one, it is that you have yet to look at one :-).
I gree in the context of the OP splitting the GND plane is a bad idea, probably very bad. My guess is the split power plane can still be made having wide enough sections so this will not be an issue, but I did not get into all the details.
Spliiting the GND plane gets useful way beyond commonplace resolution and sensitivity, this is why most people have no problem without splitting it, and being happy with their results think this is a usiversal rule. It is not.
Dimiter
------------------------------------------------------ Dimiter P> > All,
Mostly people end up with a huge loop antenna that picks up just about anything. That is because stuff will have to be connected to either side of a split, usually. Now throw something like Sutro tower into the mix and the circuit noise can reach the signal levels of a Led Zeppelin concert.
Interesting spec... Zero Offset: None
John
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
I'm sure it has something to do with the desire from many companies' management to be able to hire relatively unskilled engineers (...they're cheap!) and still have a product.
Arguably that's not a particularly awful incentive, but few companies seem to realize that the whole approach fails as soon as you want to do something just a little bit different than what the whiz-bang "all-in-one" IC does.
That's when people give Joerg a call.
Or the company I work at, for that matter. We spend plenty of time these days building radios from all the discrete mixers/amps/etc. that are now readily available, although unfortuntaely it's often difficult to compete on power relative to what some of those old Philips (NXP) parts provided. (Remeber the UAA2080? Beautiful part... very low power, good quality filters using gyrators...)
At least battery technology has progressed a bit.
---Joel
t I s
On the other hand, if your circuitry is completely isolated into physical/electrical/logical domains (such as in red/black segregation) then splitting or slotting the ground plane makes sense and may be required by the physical and/or regulatory realities.
Pretty unique, yes. And guaranteed... This is the only MCA on the market which allows you to calibrate for energy using a single point.
Dimiter
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John Lark> >
Sometimes they give me a call a bit late, after the purchasing guy became unable to source some super-duper panacea chip. Then it's often "tabula rasa", scrap the whole design and start from scratch.
Personally I am not a fan of such "panacea chips". The millisecond they lose a key account the manufacturers might stop production and soon after purge the datasheet.
However, electronics and especially the SW guys keep bloating stuff faster than battery technology can keep up with. Case in point: My early
90's laptop ran up to six hours on one NiCd charge and so I opted not to buy the extra capacity battery. Nowadays it's down to two hours with an expensive LiIon battery that has many times the capacity. And I do the same type of work on them :-)The concept of a mobile device needing a cooling fan is IMHO just plain sick.
Or take our Dimango remote doorbell. 20 bucks, 10 (!) years on the first set of batteries and no slowdown in sight. Of course, the receiver is completely discrete. This year I am going to change the batteries anyhow because they might leak just from old age.
C'mon, Didi lives and works in Bulgaria and probably speaks a language of Macedonian origin all day long. Quite different from our Anglo-Saxon language roots. It's much tougher for those guys to master English than it is for Western Europeans. Guess he meant offset from the zero-line.
Thanks Joerg,
it is not down to my English, I suppose it is good enough. I have just switched words, the spec should have been called offset-0, this is how it is known. I suppose people who know about MCAs would not pay much attention to my mistake, this is a common spec on that stuff (exactly what you guessed). I'll fix it, though.
Dimiter
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Joerg wrote:
What's the percentage tolerance spec on your zero?
John
It can be seen (and specified) as 0%. The INL and DNL are non-0, of course, so it is safe to specify that (which, in essence, is what counts - you can calibrate by 1 point without giving it much thought). The 0 is mathematically correct, and while the input data will always carry some error, it is randomized and spread over many samples (hundreds or thousands), so that specifying a non-0 number (say, 0.1% LSB...) would make no sense (and would convey perhaps the wrong message to users, they would have to look for error where there is none). The INL is within 1 LSB or so, it safely covers for the offset-0 being specified as
100% 0. So does even the DNL, BTW, I have specified a conservative number, yet the fact is it is so low I could not measure it when I did that (and I could measure 0.5% LSB DNL on my older, Wilkinson based devices).Dimiter
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John Lark> >
That's because he as afraid everyone else would go AWOL, or give you two a GI shower and blanket party. ;-)
I want the words, the prosody, not the music nor the melody for whatever voice.
See:
Well, since I can't sing I don't have any music texts. Just like I don't have sheet music.
Say Joerg,
I just thought I'd mention...
Some purchasing guy was talking with me about various parts for some project yesterday and I noticed that we're using Linear Tech's LTC1844 in numerous different products and at least so far no one's reporting seeing one misbehave. This is a 150mA LDO (90mV headroom required at 150mA, 30mV at
50mA). The data sheet has a chart that claims it's guaranteed stable so long as the output capacitance is >=1uF and the cap's ESR is
Thanks for the hint. However, quote from datasheet: "If the input supply voltage drops too low for the LTC1844 to maintain regulation, the internal feedback loop goes into dropout and the internal pass transistor turns fully on. If the input supply then suddenly rises, the output may briefly overshoot the intended output voltage ..."
Can be muffled with a big cap on the output, probably driving the p-channel into its "ouch" region. I don't really like such behavior. Nah, not my cup of tea.
I've also had my share of experiences with fast input voltage rise times. A TPS regulator reacted to that with phssst ... BANG. TI couldn't explain it, refused to give me the innards for SPICE, refused to run my circuit on their SPICE. So I just chucked it.
For a 6.5V/150mA max regulator that is quite expensive.
Hi Joerg,
Thanks for pointing that out. Wouldn't a lot of regulators (LDO and non-LDO alike) do this, though? Once you saturate your pass device, if it's slower to respond than the feedback loop, you're sunk, aren't you? (Seems like to op-amps where, once you hit the rails, pretty much all bets are off on how it behaves... although things like the outputs reversing polarity like some old op-amps did is a bit much...)
You're paying for the "very" LDO in VLDO there, I think.
---Joel
I have never seen a LM317 do that. Usually when they approach dropout LDOs steer their pass device into full conduction and naturally it'll take a while to swing back when Vin jumps back up. OTOH non-LDOs are different, they typically run out of base drive and that happens kind of gracefully. Their pass device doesn't really leave the linear range, at least not by much.
It's a bit like jet engines versus regular gas engines. When you pull the throttle on a jet engine it takes a while until it reduces thrust while a (non-turbocharged) gas engine reacts immediately.
Take a look at the right-most part of the schematic for the LM317, about in the middle of this datasheet:
People have done rather strange things with the LM317. One example is in the above datasheet on page 18 where they built a switcher with it. I've used them as AM modulators and such, usually producing some forehead wrinkles and coughing in design reviews.
When I am that tight on voltage overhead I usually build a switcher.
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