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Class D Switching Power Amplifiers and Power D/A conversion

Class D patents
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Old 14th December 2004, 09:26 PM   #11
classd4sure is offline classd4sure  Canada
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Regarding the UCD patent and Bruno's comments on it, linked to us here by Jaka Racman, is making use of a time delay simply not another form of hysteresis? Then you read the UCD patent and see "substantially free from hysteresis" which tells me it is still a part of it (at least a diode drop in the OR section of the comparator, which adds to the time delay).

If you read Bruno's reply which Jaka Racman linked to, and then his other reply to Analog Spiceman about using hysteresis with UCD:

"I know for certain that the UcD patent states the use of a comparator "substantially free from hysteresis", which means that applying hysteresis and modifying the feedback circuit in order to nullify the negative effects of this would not suffice to get from under the cover of the patent."

You'll find that in this thread http://www.diyaudio.com/forums/showthread/t-40502.html

So it would seem as I suspected, hysteresis is a part of the UCD patent as well. So I don't believe in one case you can use "substantially free from" to claim it has none, and therefore doesn't infringe, while in another case use "substantially free from" to claim that it does include it and therefore you can't get out from under it, surely it must be one or the other.

With the lack of common sense in courts though, and sometimes honesty, I sure as hell will not be the one to find out one way or the other, will you?$?

I think where UCD does deserve a patent in the rather elegant circuitry provided in it, but Takagishi should be listed as prior art and UCD as a simplification /improvement on the design.

It must be good though for everyone to loath its patent so much I don't see anyone debating TI's PWM modulator lol.

I feel the introductory paragraph of the link I posted originally in this thread really tells the story about patents though. It would seem anyone can get one if written properly, and anyone can contest it and win, if they have the money. It all comes down to who's got the green.
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Old 14th December 2004, 10:32 PM   #12
JohnW is offline JohnW  Czech Republic
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Originally posted by classd4sure
It all comes down to who's got the green.
Right On Chris!
Time is my worst enemy!
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Old 15th December 2004, 01:12 AM   #13
tiki is offline tiki  Germany
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Yet another inventor from the hifi-forum.de seems to be the writer of this:
DE19838765A1 , a self oscillating design nearly same to this of Johan Soerensen.
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Old 15th December 2004, 08:59 AM   #14
Jaka Racman is offline Jaka Racman  Slovenia
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Chris, your link is trully great. I have been searching class D patents since the days when IBM provided USPTO database sarch and I have a large pile of them, but I must say at least half of the listed patents were unknown to me. I am especially glad I have found Honeywell ampliverter (switching amplifier with HF transformer isolation) patent which predates Peavey for 10 years. I have recently found out that constructing transformers with coupling factor 0.99998 is possible and renewed interest in ampliverter design. But Peavey patent bothered me, as Bruno's patent bothered Subwo1 who also invented it, although a little later. Regarding Takagishi patent, I must give Bruno credit, he at least understands how the circuit works, while I am not sure if I can say the same for Takagishi.

John I must say I completly agree with you. If you have something new, the best way is to be quiet about it and produce it. If you must advertise it, then the best way is to take some insignificant part of your invention, invent some plausible marketing BS and throw sand into the eyes of your competition. For instance, you could advertise your excellent results are due to the superfine grain structure of the magnetic cores produced exclusively for you or something like that.

I would really like to know if any of the classD patents has been disputed in court and what were the results. It seems that today engineers need more and more legal education. I have found out that reading standards in a creative way (read: how to avoid them) is becoming more important than actual solid design work. Recently flicker standard was imposed on all medical equipment sold in EU. It affects all medical devices, also those that can not possibly operate without pulsed power consumption which would mean banning from the market. But with some twiddling with the boilerplate, standard can be avoided. What is the purpuse of this?

Best regards,

Jaka Racman
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Old 20th December 2004, 09:20 PM   #15
tiki is offline tiki  Germany
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after some discussion in the German Hifi-Forum I tried to simulate the principle of the design, suggested in the patent two posts ago. I do not know, if this principle, feeding back the pre-filter output signal to the integrator _and_ to the comparator, was invented any time before 1998. The very simple addendum to the basic hysteretic modulator seems to be clever.

As I understand it, is the reason for that added resistor to compensate the influence of supply variations on the output signal by shifting the trip points of the comparator and therefore vary the resulting pulse width. This acts very fast, the next pulse will output the correct value.
Here are the schematic and the simulation data of the basic circuit, described in the patent.
In my opinion, the simulation results make this design worth a real world try. The post filter feedback may be added indeed, to improve the overall frequency behaviour and damping factor.
I would like to hear your opinion about this trick.
Regards, Timo
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Old 21st December 2004, 03:19 AM   #16
classd4sure is offline classd4sure  Canada
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Hi Timo,

That strikes me as being very similar to Bruno's SODA amp.


It was said to sound very good, but UCD made it obsolete.
Thanks for the schematic as I wasn't at all able to read that patent you linked to.

Hanging an EF pair as current booster off of the comparator to drive the output stage might be of some help.

Nice work!


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