current dumping amplifier

[Kit]

This circuit pops up once in a while:

http://ourworld.compuserve.com/homepages/richard_brice/curdump.htm

I can recall some d*x compressors using a similar output stage but i may be wrong, (my memory is good but short) :wink: I have also seen it on the outputs of mixers.

The original circuit developed by A*C was fully discrete i think, but the basic "theory" behind the circuit was the same as the opamp version.

I wonder why you dont see this circuit more often (the patent held by A*C must have expired by now), and how come d*x and others got away with it without getting sued?

Anyway, i think its a nice, cheap circuit....

 

[bcarso]

[quote author="Kit"]This circuit pops up once in a while:

http://ourworld.compuserve.com/homepages/richard_brice/curdump.htm

I can recall some d*x compressors using a similar output stage but i may be wrong, (my memory is good but short) :wink: I have also seen it on the outputs of mixers.

The original circuit developed by A*C was fully discrete i think, but the basic "theory" behind the circuit was the same as the opamp version.

I wonder why you dont see this circuit more often (the patent held by A*C must have expired by now), and how come d*x and others got away with it without getting sued?

Anyway, i think its a nice, cheap circuit....[/quote]

Good discussion of this and other output topologies that solve problems like quiescent current stability in the late John Linsley-Hood's books, including The Art of Linear Electronics, and Valve and Transistor Audio Amplifiers. He includes some "also-ran" designs that have gotten less attention.

Sometimes people use patents by pointing out to the patent holders that prior art invalidates their claims, and that they will sue to have the entire patent removed if the patent holder sues them for infringement. I am not saying that's what happened here but it is a possibility. Happened with MTI and Audio Authority (mfg.'s of demonstration switching equipment). One has to look closely at the claims. Of course your suspect company may merely have licensed the patent.

Many of the ideas one sees heralded as new are reworkings of some of the fundamental patents of Black from the late 20'-early 30's on feedback and feedforward error correction. In another area, does anyone remember when Comlinear had patents on current-feedback amps for a while? I don't know who knocked these down, but someone sure did.

 

[Kit]

The author of the article in the link raises an interesting question at the end of the text:

"That brings me to the nub of this month's column, does patenting an invention like current-dumping really do anybody any good in the long-run?"

After all, it´s like bcarso says, not much has really happened since the 30´s.
It´s like automotive history, small improvements here and there but the basic combustion-engine remains pretty much the same.

 

[cuelist]

[quote author="bcarso"]Sometimes people use patents by pointing out to the patent holders that prior art invalidates their claims, and that they will sue to have the entire patent removed if the patent holder sues them for infringement. [/quote]

There is one thing to be granted a patent and another one to defend it. And for anyone to try to invalidate a patent based on "prior art", well in theory that IS possible, but in practive, very tough, costly and time consuming.

The reality is that patents are useful if you have big $$$ backing you. Mr Self Employed Innovator vs Clone Corporation isn't going to be pretty.

Check out Don Lancasters entertaining and enlighting website on this subject: http://www.tinaja.com/patnt01.asp

 

[bcarso]

[quote author="cuelist"]
There is one thing to be granted a patent and another one to defend it. And for anyone to try to invalidate a patent based on "prior art", well in theory that IS possible, but in practive, very tough, costly and time consuming.

The reality is that patents are useful if you have big $$$ backing you. Mr Self Employed Innovator vs Clone Corporation isn't going to be pretty.

Check out Don Lancasters entertaining and enlighting website on this subject: http://www.tinaja.com/patnt01.asp[/quote]

See also the thread in the Brewery ( http://www.groupdiy.com/index.php?topic=15141 ) about the really irritating Philips patent that is to prevent people from changing channels during commercials.

I've heard (former) high execs at the Harman empire openly say they wouldn't bother to worry about a lone inventor's patent if they thought they wanted to use it. If you are a very savvy negotiator you might persuade them to license something if you were to grant them that exclusively though.