![]() It also provided a main topic of my PhD thesis, where I also demonstrated that it could be measured directly, without being calculated from two-port parameters."Īlong with this fine page on stability factor, we now have a download spreadsheet for calculating stability factor and available gain (and many other parameters) from vector S-parameters that you can get from manufacturers' data sheets! It's called S-Parameter Utilities 101, here's a page that explains how to use it. It was a pleasant surprise to see that it had useful applications. I really have nothing useful to say about the stability factor, as for me it was mainly an exciting theoretical development, inspired by Sam Mason (who started off a paper in the IEEE "In a hundred years the earth will be covered with paper to a depth of eighty feet, and we shall all be as bald as billiard balls." Great man!). My opinion about the application of the stability factor is not worth much, as it was developed from theoretical principles, and I never used it on a real amplifier, nor did I know of anyone who had, other than reading the literature. It is interesting that a concept which was developed largely in the abstract, and with no specific applications in mind, should turn out to be useful (as indeed I hope it is). ![]() At about the same time the stability factor began to find application in microwave circuits, something I had not envisaged! My interests then turned to active filters, and eventually to speech processing (synthesis, recognition, compression - GSM), far removed from microwaves. All these transistors were measured in my high-frequency gain (f/T) apparatus. In 1963, I joined what is now British Telecomms, where a team was developing and manufacturing highly reliable silicon transistors for the first transistorised transatlantic cable amplifiers. It emerged that "f/T" was the preferred indicator of useful bandwidth, and I designed more than one method of measuring this, and also became interested in other transistor parameters, resulting in the stability factor. As the junior member, I was given the job (which no one else wanted) of devising methods of assessing their capabilities. "In 1955 I joined a team of scientists set up in London to make germanium transistors. Yet another fact that you won't learn anywhere else but Microwaves101!īelow is John's perspective on the stability factor that bears his name: Rollett's last name rhymes with wallet some engineers mistakenly try to give it French-sounding pronunciation. If the system sees an unusual but perfectly normal event, you could be in a world of hurt.īack in 2006, we contacted Microwave Hall-of-Famer John Rollett regarding his contribution to the art of microwaves (the stability factor, "K"). Treat the system delicately and it behaves (like when you RF-probe an unstable device ant it sees a broadband match). The video perfectly illustrates the idea of conditional stability. You should never tailgate a car or truck on the highway, and especially never tailgate a car or truck that is pulling a trailer. Stability is relevant in many fields, and should be a consideration in all design activity. Here's a video on how car trailers can be made conditionally stable if you put too much weight behind the axle. ![]() Here's a cool approximation for GMAX that you need to know about Here's a page on unstable amplifier examples. Click here to go to our page on Normalized Determinate Function (NDF) (new for June 2017)Ĭlick hereto go to our main page on amplifiers
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