🚀 go-pugleaf

On Thu, 12 Jan 2012 09:58:42 -0800 (PST), Bill Sloman
<bill.sloman@ieee.org> wrote:

>On Jan 12, 4:30�pm, John Larkin
><jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>> On Thu, 12 Jan 2012 02:11:46 -0800 (PST),BillSloman
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>> <bill.slo...@ieee.org> wrote:
>> >On Jan 12, 3:13�am, John Larkin
>> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>> >> On Wed, 11 Jan 2012 16:49:18 -0800 (PST),BillSloman
>>
>> >> <bill.slo...@ieee.org> wrote:
>> >> >On Jan 11, 8:22 pm, Phil Hobbs
>> >> ><pcdhSpamMeSensel...@electrooptical.net> wrote:
>> >> >> On 01/11/2012 01:43 PM, John Larkin wrote:
>>
>> >> >> > On Tue, 10 Jan 2012 18:02:50 -0800 (PST),BillSloman
>> >> >> > <bill.slo...@gmail.com> wrote:
>>
>> >> >> >> On Jan 10, 4:55 pm, John Devereux<j...@devereux.me.uk> wrote:
>> >> >> >>> Robert Macy<robert.a.m...@gmail.com> writes:
>> >> >> >>>> On Jan 10, 2:28 am,BillSloman<bill.slo...@ieee.org> wrote:
>> >> >> >>>>> On Jan 10, 7:47 am, "David L. Jones"<altz...@gmail.com> wrote:
>
><snip>
>
>> >> >> >> Motorola's ECL applications notes on board layout were rather useful,
>>
>> >> >> > Just don't trust their microstrip equation!
>>
>> >> >They looked okay in the range 50R to 75R.
>>
>> >> Yup. And they give silly, even negative, impedances for traces outside
>> >> a narrow width zone.
>>
>> >Which is more or less what I went on to say in the next paragraph -
>> >you seem to suffer from premature ejeculation.
>>
>> You suffer from nostalgia for the times, decades ago, when you
>> actually did things... most of which didn't work.
>
>I do feel a certain amount of nostalgia for the times when I did
>things - which all actually worked when management didn't cancel the
>projects before we'd got to actual hardware. Management did frequently
>decide that they couldn't sell the stuff that I was allowed to get
>working.
>
>All of this is entirely irrelevant to the observation that you went
>off at half-cock, busily saying pretty much what I'd already posted,
>but you couldn't find a way of justifying that, so you posted one more
>of your inaccurate insults instead.

I was talking about a Motorola data book, and you responded with a
personal insult. You do that sort of thing a lot here. It's not
surprising that people tended to not hire/keep you.


>
>> >> >Specialised textbooks give
>> >> >longer and more complicated expressions that give rather different
>> >> >results for microstrips and strip-line with higher and lower
>> >> >characteristic impedances.
>
><snip>
>
>> >At current ECLinPS speeds everything gets averaged over a few
>> >millimetres of track. The extra capacitance implicit in a right-angle
>> >bend on a 5OR track might be perceptible, but you can pretty much
>> >eliminate it by chamfering the corner, or making two 45-degree bends
>> >in quick succession.
>>
>> That's what the ancient Moto book said. It was stupid at 10K speeds
>> and it remains stupid at EclipsPlus speeds. I can barely discern a
>> right angle with a zoomed-up 30 ps TDR edge. The weave of the
>> fiberglass changes the impedance more than a sharp corner. Vias are
>> hugely more important than right angles.
>
>Obviously.
>
>I'm a bit surprised that you are bothering to do time domain
>reflectometry on FR-4 boards. Rogers make a bunch of substrates that
>work rather better at very high frequencies. A Cambridge Instruments
>we made the outer layers of six layer boards for the GaAs parts with
>isocyanate-resin-bounded Teflon cloth. The inner layers (that weren't
>exposed to the GaAs signals) were regular FR-4 which kept the board as
>a whole rigid - they were triple extended Eurocards and we didn't want
>them flopping around.

Probably the cost of the boards contributed to the overall project
failure. We do picosecond stuff on FR4 all the time. I do TDR and
other tests on boards so I can understand them and learn stuff, and
make sure my suppliers are doing the stackups right, and so that I can
separate what matters from the masses of hand-waving "theory" that
folks like HoJo sell.


>
>Our printed circuit board supplier charged us extravagantly for the
>boards - he had to buy a lot more of the isocyanate-resin-bonded
>Teflon cloth substrate than he need to make up our first batch of
>boards, and he knew we were pushing the state of the art, and - very
>wisely - wasn't prepared to wait for us to order a production batch of
>boards to cover the expenditure.

The only thing you were pushing the state-of-the-art on was expense.
The Moto ECL and GBL GaAs parts would work fine on FR4.

The exotic substrates seldom make sense for digital logic. If you have
a *lot* of layers, over 8 maybe, a lower Er is handy to keep the trace
widths and impedances practical. 

RF stuff can sometimes justify exotic laminates, to keep filter Qs up
and noise figures down. High thermal conductivity laminates could be
interesting.

John