High Frequency Response of BJT | Multistage Amplifier Part 2 | Electronic Devices and Circuits 2 | Summary and Q&A

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April 9, 2022
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High Frequency Response of BJT | Multistage Amplifier Part 2 | Electronic Devices and Circuits 2

TL;DR

Learn about the high frequency response of BJT amplifiers and how to calculate the higher cutoff frequency.

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Key Insights

  • ✋ BJT amplifiers have capacitances that affect their high frequency response.
  • ✋ Certain capacitances become short circuits at high frequencies, while others form stray capacitances.
  • ⚡ The higher cutoff frequency needs to be determined to design a BJT amplifier with high voltage gain.
  • ✋ The AC equivalent model helps in analyzing the high frequency response using RC circuits.
  • ✋ Calculating the higher cutoff frequency involves considering the total capacitance at the input and output side of the AC equivalent model.
  • ✋ The minimum value of the higher cutoff frequency is chosen as the desired cutoff frequency for the amplifier design.
  • ✋ Understanding the high frequency response of BJT amplifiers is important for circuit design and analysis.

Transcript

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Questions & Answers

Q: What happens to the capacitances in a BJT amplifier at very high frequencies?

At high frequencies, certain capacitances become short circuits, while others form stray capacitances.

Q: What are the capacitances responsible for the higher frequency response in a BJT amplifier?

The capacitances between the base and collector, collector and emitter, and base and emitter are responsible for the higher frequency response.

Q: How can we model the high frequency response of a BJT amplifier?

An AC equivalent model can be used, where certain capacitances are considered and the resistor-capacitor (RC) circuit is analyzed.

Q: How can we calculate the higher cutoff frequency of a BJT amplifier?

The higher cutoff frequency can be calculated by determining the total capacitance at the input and output side of the AC equivalent model and using the formula 1/2πRC.

Summary & Key Takeaways

  • BJT amplifiers have capacitances that affect their high frequency response.

  • At high frequencies, certain capacitances become short circuits, while others form stray capacitances.

  • To design a BJT amplifier with high voltage gain without damaging the BJT, the higher cutoff frequency needs to be determined.

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