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.

Transcript

hello friends in this particular video we will learn the high frequency response of bjt amplifier where we'll have to learn few different concepts and we'll have to apply these concepts to find out the higher cutoff frequency so that we can easily get the mid voltage mid frequency range voltage gain and also we can draw the complete frequency respo... Read More

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.

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.