Amplifier Concepts

Amplifier Concepts

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The β transform greatly simplifies open-loop amplifier circuit analysis and makes the transresistance method possible. We now examine circuits with more complex topologies. It is common for transistor amplifier stages to have a significant forward transmittance through ro. This results in parallel forward paths. Parallel c-e or c-b resistance causes bilateral signal flow with a combination of feedback and multiple forward paths. The dual forms of the reduction theorem, source-shifting, and the substitution theorem expand the power of circuit analysis, allowing the reduction of active amplifier stages to voltage and current dividers. These methods, however, are not sufficient in themselves. In the next chapter, feedback theory is developed - another analytic method that greatly simplifies circuit analysis. The methods of this chapter are based on transformations of networks that eliminate dependent sources and result in a single network. Feedback theory reduces signal paths (transmittances) instead, resulting in a single transmittance.

Chapter Contents:

  • The Reduction Theorem
  • μ Transform of BJT and FET T Models
  • Common-Gate Amplifier with r 0
  • Common-Source Amplifier with r 0
  • Common-Drain Amplifier with r 0
  • FET Cascode Amplifier with r 0
  • Common-Base Amplifier with r 0
  • CC and CE Amplifiers with r 0
  • Loaded Dividers, Source Shifting, and the Substitution Theorem
  • Closure

Inspec keywords: amplifiers; circuit feedback; bipolar transistors

Other keywords: bipolar junction transmitter; BJT; complex topology; current dividers; reduction theorem; bilateral signal flow; substitution theorem; source-shifting; amplifier concepts; open-loop amplifier circuit analysis; parallel forward paths; transistor amplifier; active amplifier stage reduction; feedback; β transform; c-b resistance; feedback theory; transresistance method; parallel c-e resistance; multiple forward paths; voltage dividers

Subjects: Amplifiers; Bipolar transistors

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