by Butch Shadwell
I am so tired of all of the typographical errors and occasional grammatical faux pas that I read in these columns. I think somebody should do something about it.
Over the years I have invented quite a number of new technologies, circuits, systems, algorithms, etc. A small percentage of them have been patented with the US Patent and Trademark Office. The thing is that whenever I am filing for a patent on something, I suddenly find that I have a lot of writing to do. And it’s not only technical writing, but rather a strange legalistic version of a technical description. Another thing about writing patents is that you need to describe every detail of your invention so that someone with ordinary skill in the art can make one for themselves. The problem arises when you find out that the patent examiner assigned to review your claims, may not have that skill level. So you have to keep on writing.
I used to do R&D in electronic warfare. I designed a circuit once that used the voltage across a diode junction to get the log of an input sine wave function. That signal was amplified 2X and then that voltage was applied to the base of a bipolar transistor, where the collector current is proportional to antilog of the change in voltage applied to the base. What does the voltage across the collector resistor look like? In the old days we did some pretty cool math with analog components. Assume that all four quadrants are covered.
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The names of correct respondents may be mentioned in the solution column.
* We seemed to have gotten behind on the challenges and answers, so here is the last few. As of September, the August edition was the last one that Butch had sent out. Figure that one out:) - Webmaster.
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1 comment:
Last monthís BTC was a bit easier than I like, but I was having a worse time than usual coming up with an appropriate problem. I decided to ask about LED biasing as follows: ìÖ a circuit once that used the voltage across a diode junction to get the log of an input sine wave function. That signal was amplified 2X and then that voltage was applied to the base of a bipolar transistor, where the collector current is proportional to antilog of the change in voltage applied to the base. What does the voltage across the collector resistor look like? ... Assume that all four quadrants are covered.î
I gave a lot of information in this problem in an attempt to keep it as simple as possible. In fact I try to keep these things simple enough to do in your head without any reference material at all. In this problem I describe a circuit configuration that takes the log of an input signal, then doubles it and takes the anti-log. This is the mathematical equivalent of squaring the input signal. If the input signal is a sine wave (Asin(wt)) then the output should be (Asin(wt))^2. The answer to squaring a sine wave is A^2/2(1-cos(2wt)). If A equals 1 then sin^2 (wt) = Ω(1 - cos (2wt), an identity I am sure you have all learned at some point in the distant past. The answer to the question is that the output is a sine wave at twice the frequency of the input sine wave, in phase, two for one. But I bet you already knew that.
- Butch
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