Maker Pro
Maker Pro

PCB power planes?

  • Thread starter Martin Griffith
  • Start date
M

Martin Griffith

Jan 1, 1970
0
2.1.1 is insane. They can't make up their mind whether to use 0r
resistors or beads, so they are still guessing.

Splitting grounds is usually a bad idea. Except when it's a terrible
idea.

Fig 5.3 looks so weird to me that I assume PDF rendering errors. Does
anyone else see huge black triangles?

2.1.2 suggests sequencing or possible latchup problems. Be careful
here; get more info maybe.


John
I get the same triangles, silly idiots for letting something out like
that in a ref. design.
I don't think I need all the extra bits, just 1 vid in and an AVR or
8051 to control it, so I was just going to have a vdd and gnd copper
flood on the inner layers, get some cheap boards done to test.


martin
 
R

Rich Webb

Jan 1, 1970
0
Fig 5.3 looks so weird to me that I assume PDF rendering errors. Does
anyone else see huge black triangles?

Yes, with both the Foxit and PDF-XChange viewers so it's probably in the
original.
 
E

Eeyore

Jan 1, 1970
0
John said:
Splitting grounds is usually a bad idea. Except when it's a terrible
idea.

Except when it's audio of course and you don'y want digital return
currents you can hear in the audio ground. In which case pkysically
separated but carefully linked planes are the way to go in order to
direct the currents where you want them to go rather than randomly
anywhere.

Graham
 
M

Martin Griffith

Jan 1, 1970
0
Except when it's audio of course and you don'y want digital return
currents you can hear in the audio ground. In which case pkysically
separated but carefully linked planes are the way to go in order to
direct the currents where you want them to go rather than randomly
anywhere.

Graham
Ha.. I remember a student who said he could make a small audio desk
with the equalisers using MF10's.
Never saw him again....I wonder why?


martin
 
E

Eeyore

Jan 1, 1970
0
Martin said:
Ha.. I remember a student who said he could make a small audio desk
with the equalisers using MF10's.
Never saw him again....I wonder why?

Was that the NatSemi ? switched capacitor filter ?

No surprise there !

Graham
 
E

Eeyore

Jan 1, 1970
0
Joerg said:
Weird. But I'd be a lot more concerned about figure 5.2. Splitting
grounds is rarely a good idea. Might also blow the EMC cert.

Depends how you treat them ! Respect pays dividends.

Graham
 
J

Joerg

Jan 1, 1970
0
Eeyore said:
Depends how you treat them !


Even a nice application of Olde English furniture polish won't help :)

... Respect pays dividends.

Can you tell that to the current generation of kids?
 
J

Joerg

Jan 1, 1970
0
Eeyore said:
Was that the NatSemi ? switched capacitor filter ?

No surprise there !

You can design rather excellent audio gear with S/C filters. BTDT. Ok,
not audio but audio range. It was a Doppler receiver for medical
ultrasound. Zero through about 25kHz, dynamic range from here to the
Klondike. Noise from clocks and stuff: None. Sold like hotcakes, still
in use.

The only reason why S/C filters fell from grace with guys like us was
cost. They probably tried to maintain fat profit margins and that backfired.
 
J

Joerg

Jan 1, 1970
0
Joel said:
So you went back to continuous time filtering? Since it doesn't appear to me
that the margins on DSPs are in any way lower than those on switched cap
devices...

Actually they are. You can get a TMS320 for less than four bucks. But
mostly I did go back to continuous time filtering. When it had to be
flexible sometimes heterodyne schemes. Mix to wherever filtering is easy
(meaning cheap ...) and then back.

Then there is the lost art of wave digital filters. Only few people know
it and you can get away with very cheap uC sans HW-multiplier.
 
S

Scott Seidman

Jan 1, 1970
0
Noise from clocks and stuff: None.

That's not my experience. Switched cap filts are famous for clock bleed
through, and you need to be sure your circuit can tolerate this. The clock
frequency is usually an order of magnitude or more higher than the filter
freq, so you can usually filter out the bleedthrough with an RC.
 
J

Joerg

Jan 1, 1970
0
Scott said:
That's not my experience. Switched cap filts are famous for clock bleed
through, and you need to be sure your circuit can tolerate this. The clock
frequency is usually an order of magnitude or more higher than the filter
freq, so you can usually filter out the bleedthrough with an RC.

Yes, you must filter that out. Sometimes. There are apps where spectral
components above 100kHz just don't make a difference. Plus the supplied
clock shall be squeaky clean. Marvelous concept but IMHO the marketing
guys killed it. Tried to make a killing with margins and then the market
kind of imploded around them.
 
S

Scott Seidman

Jan 1, 1970
0
Also famous for aliasing inputs, aliasing power supply noise, and
making a heap of noise of their own. But the programmability is nice.

The world needs a general-purpose programmable continuous-time lowpass
filter IC. Really.

John

They get terribly expensive, even for non tunable filters. I've been
using Frequency Devices single freq analog Bessels, and they run about
$100 a channel.

Krohn-Hite used to make an 8-pole tunable analog filter but it was bench
gear, not an RC.

I think the closest you're going to get today would be biquad stages that
use resistors to tune them, and programmable resistors. At least that's
an all IC approach, and you wouldn't need a billion-stage stacked switch.

Aliasing inputs, by the way, can come from surprising sources. People
tend not to think about bleed through on chopper amp clocks, for example,
but it's there.
 
J

Joerg

Jan 1, 1970
0
John said:
Also famous for aliasing inputs, aliasing power supply noise, and
making a heap of noise of their own. But the programmability is nice.

Look at the bright side: You can make really nice mixers and stuff with
them. If they just weren't so darn expensive.

The world needs a general-purpose programmable continuous-time lowpass
filter IC. Really.

If you use the R2R ladders of DACs you could make one around chips like
these:
http://datasheets.maxim-ic.com/en/ds/MAX274-MAX275.pdf

Of course, then you'd be on the phone with Rebecca all the time.
 
J

Joerg

Jan 1, 1970
0
Joel said:
Yeah, although can you get even within even an order of magnitude in group
delay (12us w/100kHz cutout) with a $5 DSP? :)

(While I haven't personally used that IC, other people here have, and I'm told
that's why -- they're trying to minimize some big audio system's group delay,
making it something like <1ms total.)

That's the crux with DSP, they often can't do that. This is where wave
digital filters come in handy but youngsters don't have the foggiest
what that is or think it's some tuning device for a surfboard.
 
J

Joerg

Jan 1, 1970
0
Joel said:
They are few -- if any? -- undergraduate EE curriculums that even mention
switched cap design... it's pretty much all DSP and lumped-element filters
these days.

Shhht! Don't tell. Keeps us busy :)

I've read the Fettweis paper on WDFs -- I think I posted a copy to ABSE at
some point? -- but I've never had a good application for them. I should
definitely revisit the topic as I didn't realize the group delay could be so
small.

You need to select a processor that can do stuff like fetch, shift and
shift-add in very few machine cycles, ideally in one. Should be 16-bit,
too, but that's no big deal anymore these days.

AFAICT after Professor Fettweis retired the usual happened. This whole
research area became unglued and withered. It's sad, there is hardly any
continuance in academia. That's what I like about working in industry,
you continue the product lines whether you like it or not. Better for
the customers.
 
Top