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How to design discrete circuits for transistor beta changes?

  1. Nov 8, 2015 #1
    In my circuits/active devices course we had to make amplifier designs with various type of transistors (BJT, JFET, MOSFET). In each design the transistor beta parameter played an important role in deciding which resistors to use in the final amplifier circuit. This beta parameter changes widely from one transistor to another...

    My question is, if I wanted to manufacture a circuit that has discrete transistor components, how are these fluctuations in the beta parameter of all these transistors compensated?

    For example: If two 2N3904s are used and their betas were, say, 100 and 130, would the resistors and caps in the design have to cater to each individual transistor, therefore CHANGING the design values of the circuit for each individual product? Or are there some useful circuits that get around this pitfall? Or are there other techniques that I don't see?
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  3. Nov 8, 2015 #2


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  4. Nov 8, 2015 #3


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  5. Nov 8, 2015 #4


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    Pretty much the first topic covered in BJT amplifiers in school was designing in such a way as to minimize the effect of changing beta.
  6. Nov 12, 2015 #5
    Check out "The Art of Electronics" by Horowitz and Hill. They've just issued a new edition. It's full of helpful and practical approaches to problems like this. It starts right at the beginner level but works right through things like transistor & FET biasing and reducing beta and gm sensitivity. They cover a multitude of topics and have all kinds of real-world examples, part numbers, and practical tips. The tone is informal and entertaining too.
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