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Originally Posted by John Hardy Paul Wolff said:
Deane did NOT use the emitter inductors to lower the gain at higher frequencies. The emitter inductors have absolutely nothing to do with lowering the gain at higher frequencies. They increase the gain at lower frequencies to reduce the noise voltage in the audio bandwidth. It is the emitter resistors that determine the high-frequency gain and stability of the stage.
To quote from Deane's paper about the 990:
Thank you.
John Hardy
The John Hardy Co. www.johnhardyco.com |
Now that you got me started again, here is a QUOTE from the patent (4287479 if you want to read it yourself, you will need a quicktime viewer. It is on the 1st image page):
...Each reactive network in the emiter circuit comprises an inductor and a resistor, arranged in a shunt configuration, whearby at
low frequencies the first stage has a relitively high gain and generates reletively low noise, and whereby at
high frequencies the first stage has relitively low gain and the amplifier circuit has sufficiant phase margin to insure stability...
Am I new here?
Also, the patent really is about the way the inductor is wound, as the ADI circuit designed by Dick Berwin in 1966 clearly shows a reactive network and a resistor in the emiters to lower the noise by lowering the gain at higher frequencies. Kind of hard to beat that unless you include a special way of making a choke, which then makes it unique. So in other words, if someone were to put regular chokes in the emiters, they would not violate the patent, because of proof of prior art. The earliest reference to prior art by Dean is in 1968, but no reference to the unpatented use of inductors to lower noise and gain in 1966. Berwin was a well known designer in those days.
From Dean's patent:
"...the inductor in each of said first and second reactive networks includes a ferrite bead having a succession of spaced, substantially parallel holes formed therein, and a wire wound in an alternating fashion through the successive spaced holes of said ferrite bead, and..."
By specifying the "requirement" of the custom choke, he gets the patent. If the examiner had known about the Berwin op-amp, the patent scope would have been reduced to only the choke.
If any of you have ever written a patent, you know what I mean. If you haven't, you should so you can see how poetic you have to be to fool the examiners.
Oh well.
boy am I going to get a lot of sh*t for this one...