Bob Cordell Interview: Negative Feedback - Page 101 - diyAudio
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Old 6th July 2007, 08:35 PM   #1001
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Quote:
Originally posted by G.Kleinschmidt



And another thing or two with regards to noise;
The I-mirror loading of each LTP cancels the noise generated in the LTP tail current sources. The symmetrical topology of the current source (Q3, Q4, R7) that provides the symmetrical VAS biasing voltages across R22 and R25 injects a common noise signal into the base of each VAS transistor. Since the VAS is differential, the noise of this current source is cancelled as well.

I don't see noise being a problem here.

Hi Glen,

These are good points. I've thought about your circuit some more and agree that it is an improvement on approaches that do not use the current mirror, even though it adds some complexity.

I'm still concerned about the limited amount of first-stage gain one gets in front of the VAS in these circuit architectures, but recognize that no circuits are without limitations and a lot is a matter of architectural preference.

Its really a shame the the circuit with current mirrors by Randy Sloane doesn't work! Indeed, I guess the limitation placed on the gain by the resistor in both your circuit and the conventional circuit is what ends up making the VAS standing current definable. Your circuit approach appears to give the designer more flexibility in choosing the value of that gain-defining resistance. In cases where offsets among the input differential pairs can be held very small, the designer may be free to use a larger value of this resistance and still have a reasonable tolerance on the resulting VAS standing current.

Cheers,
Bob
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Old 13th July 2007, 03:02 PM   #1002
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Quote:
Originally posted by jacco vermeulen
The Candyman resumé =>HERE

This patent by Bruce Candy of Halcro is a curious one. It is so, because it does not employ error correction of the Hawksford variety.

His earlier error correction patent, where he merely added an output-bootstrapped power supply to the Hawksford scheme, was #5,892,398. Most of us have assumed that he has based all or part of his amplifier line on this patent.

This later patent uses, instead of HEC, a high-order feedback scheme (at least third order) with enormous amounts of global as well as local feedback. I honestly don't know if he has switched to this non-HEC scheme in his later amplifiers.

It is also curious that this later patent is the first time he mentions the relevent HEC prior art, including that of Hawksford and myself. Go figure...

Cheers,
Bob
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Old 14th July 2007, 02:08 AM   #1003
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Quote:
Originally posted by Bob Cordell
This later patent uses, instead of HEC, a high-order feedback scheme (at least third order) with enormous amounts of global as well as local feedback. I honestly don't know if he has switched to this non-HEC scheme in his later amplifiers.

It is also curious that this later patent is the first time he mentions the relevent HEC prior art, including that of Hawksford and myself. Go figure...
Cynical observers would be tempted to conclude that once
HEC has been superceded, it is mentionable.

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Old 15th July 2007, 05:16 PM   #1004
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Quote:
Originally posted by Nelson Pass


Cynical observers would be tempted to conclude that once
HEC has been superceded, it is mentionable.


When I'm feeling cynical I figure that Candy knew that he would never have been granted that patent if he had disclosed the prior art.

Cheers,
Bob
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Old 15th July 2007, 05:59 PM   #1005
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One of the requirements of a patent is disclosure of prior art,
but I don't believe you are required to perform a search, so not
searching (or more specifically, not finding) is perhaps a functional
strategy, the patent office being what it is these days.

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Old 15th July 2007, 06:16 PM   #1006
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Quote:
Originally posted by Nelson Pass
One of the requirements of a patent is disclosure of prior art,
but I don't believe you are required to perform a search, so not
searching (or more specifically, not finding) is perhaps a functional
strategy, the patent office being what it is these days.


The requirement is that of disclosing KNOWN and RELEVANT prior art.

The Patent Office used to have a "fraud czar" to spank some of these characters that failed to report. Before I retired, I couldn't get the powers-that-be to give a damn about an inventor failing to disclose his OWN prior art. I think we should assume he knew about that. I think the Office just regards the issue as the inventor's problem if he tries to enforce any granted patent. In the mean time, our government collects a maintenance tax on the issued patent. A LOT of things changed around there when maintenance fees became a cash cow!
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Old 16th July 2007, 02:28 AM   #1007
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Quote:
Originally posted by Nelson Pass
One of the requirements of a patent is disclosure of prior art,
but I don't believe you are required to perform a search, so not
searching (or more specifically, not finding) is perhaps a functional
strategy, the patent office being what it is these days.


Hi Nelson,

He would not have had to perform a search. It is inconceivable that he was unaware at the time (of his earlier error-correction patent) of the work done by Hawksford and myself, which predated by about 10 years. The circuits he shows in that first patent are conspicuously similar to the earlier work, even down to the way in which the EC circuit was compensated.

Cheers,
Bob
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Old 16th July 2007, 02:43 AM   #1008
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Isn't patenting a product different from patenting the invension?
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Old 16th July 2007, 08:01 AM   #1009
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Overhere the three criteria to apply for a patent are:
1-Novelty of the invention
2-Inventivity
3-Industrial application
No3 states that an invention has to be a functional product.

Different are : shape and label design patents, mainly the duration of the patent, validity of 14 years in the US.(author IP rights belong to a different club i think)
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Old 16th July 2007, 09:51 AM   #1010
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4- The invention shall not be obvious for the person skilled in the art
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