🚀 go-pugleaf

On 2012-01-10 17:50, John Larkin wrote:
> On Tue, 10 Jan 2012 17:29:35 +0100, Jeroen Belleman
> <jeroen@nospam.please> wrote:
> 
>> John Larkin wrote:
>>> On Tue, 10 Jan 2012 01:28:22 -0800 (PST), Bill Sloman
>>> <bill.sloman@ieee.org> wrote:
>>>
>>>> On Jan 10, 7:47 am, "David L. Jones" <altz...@gmail.com> wrote:
>>>>> Just thought some might be interested in hearing our recent guest on
>>>>> our Amp Hour radio show, Dr Howard Johnson of "Handbook of Black
>>>>> Magic" fame[...]
>>>
>>> Yeah, his book is half nonsense. If you can tell which half is which,
>>> you don't need the book. His ideas on "return currents" and bypassing
>>> are absurd. And the writing is dreadful.
>>
>> I haven't got the book handy, but I'll pick it up tomorrow or so.
>> Do you mind expounding on why his "return currents" make no sense?
>> Did he mean something different from image currents?
> 
> He says that a transmission-line pcb trace must always be "referenced"
> to the same "return current" plane it started with and shouldn't pass
> through vias to become referenced to a different plane, or else the
> return currents will get confused or go on strike or something. If
> that were true, 98% or the multilayer boards on Earth would quit
> working.
> 
> He also says that you should add bypass caps and stitching vias to
> conduct these return currents whenever a trace does via to a different
> "reference plane." 
> 
> All silly.

Ah, yes, I agree with you there. Mostly anyway. Capacitance between
planes should be plenty to take care of that.

I *did* have this amplifier with a ridiculously high gain that
wouldn't keep still with its output trace running over the V+
plane. The problem vanished when I made it run over a GND plane
instead. Then again, there were a few other layout tweaks that
may have contributed to fixing it.

Jeroen Belleman