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Old 29th June 2012, 08:29 PM   #2621
MiiB is offline MiiB  Denmark
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Not to spoil the shutting down of the feedback discussion completely, but to state how I see things...I may be completely of track...but this makes sense to a mechanical guy...

Feed back compares levels...A real time scale lock...Trouble is that it comparing slightly time shifted levels...and with increasing frequency this time shift matters more and more and hence the distortion increases with frequency...makes perfect sense to me...feedback is not comparing wave-forms, it's comparing levels.
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Old 29th June 2012, 08:43 PM   #2622
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Quote:
Originally Posted by MiiB View Post
Not to spoil the shutting down of the feedback discussion completely, but to state how I see things...I may be completely of track...but this makes sense to a mechanical guy...

Feed back compares levels...A real time scale lock...Trouble is that it comparing slightly time shifted levels...and with increasing frequency this time shift matters more and more and hence the distortion increases with frequency...makes perfect sense to me...feedback is not comparing wave-forms, it's comparing levels.
Fully agree when you replace time shifted by phase shifted

jan
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Old 29th June 2012, 08:46 PM   #2623
MiiB is offline MiiB  Denmark
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time is phase...or..??
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Old 29th June 2012, 08:50 PM   #2624
sonnya is offline sonnya  Denmark
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Originally Posted by Edmond Stuart View Post
Hi Sonnya,

At the moment I can't show you recent work yet*, but if you like, have a look at some outdated stuff from the past: here and here.

* At the moment I'm busy with translating a MicroCap file to FreePCB (PADS format) and after that, drawing the PCB itself. A hell of job and expensive too (to get an impression see the thumbnail of the schematic below).
As you see, it's the opposite of a Simple Symmetrical Amplifier.
edit: It's like a V8 engine with two desmodromic valves per cylinder.

Cheers,
E.
Or a pushpull driver for every mosfet. Your front end is vfb where i am more to cfb but complexity is the same in My cfb design with an modificede current mirror.

Go for orcad. In Denmark they have a lease plan. Then you Can combine pspice with sch and pcb. Or the more expensive dxdesigner with hyperlynx and pads interactive router
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Old 29th June 2012, 08:59 PM   #2625
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Actually phase is a bit faster then local time but does not cary information.
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Old 29th June 2012, 09:01 PM   #2626
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Can be ....
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Old 29th June 2012, 09:57 PM   #2627
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Default "pour les couilles du pape"

Quote:
Originally Posted by MiiB View Post
[...]
Feed back compares levels...A real time scale lock...Trouble is that it comparing slightly time shifted levels...and with increasing frequency this time shift matters more and more and hence the distortion increases with frequency...
Aaaaaaargh! Am I talking here "pour les couilles du pape"*?

If you are talking about a time shifted signal (inside a feedback loop), thus without amplitude roll-off at higher frequency, such system is unstable (by definition). If, under marginal conditions, it might happen to be stable, then it does not increase the distortion.

Quote:
makes perfect sense to me...feedback is not comparing wave-forms, it's comparing levels.
True.

Anyhow, you folks make me really angry, as you refuse to understand or accept that time shift is NOT the same as phase shift.

* In Dutch: "Voor de kat zijn kut".
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Old 29th June 2012, 10:21 PM   #2628
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Quote:
Originally Posted by Edmond Stuart View Post

Anyhow, you folks make me really angry, as you refuse to understand or accept that time shift is NOT the same as phase shift.

* In Dutch: "Voor de kat zijn kut".
You are right,
Time shift description makes the feedback limitation much more easily understandible...
Phase shift issues in feedback are much more complicated to explain as they are also time shift but are also frequency depandent and involve additional compexity..
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Old 29th June 2012, 10:26 PM   #2629
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Originally Posted by sonnya View Post
Or a pushpull driver for every mosfet.
Right. BTW, the bunch of extra trannies cost me virtual nothing.

Quote:
Your front end is vfb where i am more to cfb but complexity is the same in My cfb design with an modificede current mirror.
If you need the ultimate speed, admitted, go for cfb. But in my case I finally opted for the lowest possible distortion (THD-20k of the front-end is ca. 50 ppb) and lower offset.

Quote:
Go for orcad. In Denmark they have a lease plan. Then you Can combine pspice with sch and pcb. Or the more expensive dxdesigner with hyperlynx and pads interactive router
Orcad? No way (I have used it once). I stick with MC, the most user friendly, versatile and fastest simulator you can get (it's written by real programmers, thus it's not bloat ware). The only drawback is that it is not integrated with a PCB package, though it does a translation to different PCB packages. But in most cases you have to (re-) define (or assign) the shapes and pins of the components (in conformance to names of the target S/W).
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Old 29th June 2012, 10:30 PM   #2630
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Phase shift, we could even say frequency dependent time shift because of circuit's LC (not Lazy Cat) characteristics, to put Edmond's and Mikelm's explanations on common denominator, just in a sense to make an explanation easier.
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