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Class D Switching Power Amplifiers and Power D/A conversion

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Old 8th April 2004, 09:28 PM   #21
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Hi Patrik,

Fig. 13 from the aforementioned patent has nothing to do with schematics posted. Maybe you were thinking of Fig. 10. Here is actually shown that the feedback is taken from the switching stage with additional low pass filters in feedback and forward paths.

The very reason I am disputing your opinion, is that I came to the Putzeys circuit by thinking how to improve ICEpower VCOM. I thought there is no reason to use low pass filtered output from switching stage, when there is already output filter. Let' s take feedback from output stage.

Only later I realized that this is the same circuit that Subwo1 had already posted. The only difference was that I thought that feedback compensation resistor RL was not necessary, while Subwo1 even included this one. We discussed this in the middle of a very long thread.

I also share Subwo1's opinion about Putzeys patent, but based on my post in another thread. It shows picture from US patent 6,489,841 which predates Putzeys patent. But then again, actual patent claims my be different.

The sad fact is that this circuit has to be the simplest possible implementation of the class D amplifier, and it is not in the public domain.

Best regards,

Jaka Racman
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Old 8th April 2004, 10:53 PM   #22
subwo1 is offline subwo1  United States
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Hi Pabo,
in my opinion, any 1 resistor, 1 capacitor Schmitt oscillator and the classic capacitor-delay-on-inverting-pin opamp type are basically the same circuit. The output is taken at the input pins of each. For that matter, an unstable audio amp that oscillates is basically the circuit also, just add the output filter before the feedback to slow down the period and to smooth the output. Maybe I just oversimplify things, dunno.
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Old 9th April 2004, 05:18 AM   #23
IVX is offline IVX  Russian Federation
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Many doubts, that PHILIPS has plans to pursue somebody, which will be using them patented RC (actually one res & one cap) network, probably they wanna just protect himself from outside patents attack. Usually the PHILIPS business it's a tonnes of chips for TV, homecinema, audio etc. (excluding I2C precedent some years ago, as me remember )
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Old 9th April 2004, 07:26 AM   #24
subwo1 is offline subwo1  United States
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Sounds like a reasonable assessment, IMHO.
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Old 9th April 2004, 07:51 AM   #25
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Quote:
Originally posted by Jaka Racman

<snip>
I also share Subwo1's opinion about Putzeys patent, but based on my post in another thread. It shows picture from US patent 6,489,841 which predates Putzeys patent. But then again, actual patent claims my be different.
<snip>
I'd like to throw in my cent's worth here. The Takagishi patent explicitly uses hysteresis (Vref1+/-dV in the comparator feedback in the picture). This is unnecessary - the delay of the power chain is wholly sufficient to obtain a well defined oscillation. Adding hysteresis will actually produce unwanted extra frequency modulation and adversely affect large-signal linearity of the modulation scheme. Unfortunately for MPS, the patent makes the hysteresis part of its claims.
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Old 9th April 2004, 09:22 AM   #26
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Hi Mr. Putzeys,

While Takagishi has been granted three patents on the same circuit it is true that all of them use hysteretic comparator. I stand corrected.

I would hovewer like to use this chance and hear your opinion if posted circuit infringes your patent. IMHO it improves on your circuit in two ways:

first it prevents power supply pumping at low frequencies (well known fact that can be considered public domain)

second, by using CC coupling capacitor in filter it forces both halfs of the amplifier to oscillate at the same frequency and phase. This canceles ripple in differentially coupled load as can be seen in this simulation .

Since I have no commercial interest in this design, I would like to proclaim it as public domain, but only if you feel that it does not infringe your patent.

Best regards,

Jaka Racman
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Old 9th April 2004, 10:02 AM   #27
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Quote:
Originally posted by Jaka Racman
<snip>
Since I have no commercial interest in this design, I would like to proclaim it as public domain, but only if you feel that it does not infringe your patent.
Hi,

Not so much up to me to decide that, it's Philips who decides to what extent to enforce the patent.

Legally speaking, when someone invents an improvement on a patented invention they can patent the improvement with reference to the original patent. The improvement is then their ip. License fees are split between the holder of the original patent and the holder of the new patent in an arrangement to be negociated among those two parties.

In this particular case, the improved circuit can no longer be patented because by the simple act of publishing it on this forum you've already made it public (well I've seen similar things float around before too). Another reason would be that we have already been using that arrangement in products (philips mini sets, nothing fancy) for quite some time.

Now "public domain" and "public domain" are two things. Inventors don't normally enforce their patent rights on individual experimenters. That would go against the spirit of the system, which is to encourage information sharing while still allowing inventors to get a fair return for their work. Now, if a company were to use the circuit in mass-produced items, Philips would most certainly knock on their door for royalties based on the original patent. In short, patenting means "to publish while asserting your rights as an inventor."

All this means nobody will stop you from actually publishing circuits based on a patented invention. Making money from them is a different affair.

Cheers,

Bruno
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Old 9th April 2004, 10:51 AM   #28
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Quote:
Originally posted by subwo1
The circuit Jaka Racman posted an image of seems so obvious and universal that it should not be patented <snip>
We might want to make a distinction between obvious and simple. When many people are trying out all sorts of ideas or variations without anyone actually heading straight for the prize, it becomes hard to argue the idea was obvious. Simple, yes.
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Old 9th April 2004, 03:36 PM   #29
subwo1 is offline subwo1  United States
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Default Reply to Bruno Putzeys

Thank you, sir, for clarifying about the distinction. I most certainly have been know to get carried away with my phrasing at times.
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Old 9th April 2004, 08:32 PM   #30
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Hi Mr. Putzeys,

while I admire your work, I can not share some of your legality thoughts.

First I find very unlikely that anyone patenting improved circuit would be willing to share royalities with the holder of the patent that was improved. Anyone writing a patent application is smart enough to try to present his invention as something completly new and best thing since sliced bread. For one thing, I do not think that you consider your circuit as an improvement of Takagishi patent, and that Philips is willing to pay royalities to MPS.

Second, for real patent protection, WO (PTO) patent number means almost nothing. It only means that you have 18 months priority time to file national patent applications for each country where you expect your sales profit to be larger than the cost of the national patent application and maintaining fee. While this would be no problem for Philips, I still think they will not do that in every country of the world.

Best regards,

Jaka Racman
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