AC Analysis of CS Amplifier (with Bypass Capacitor ) | Electronic Devices and Circuits - 1

TL;DR

This video provides a comprehensive analysis of the AC analysis of a common source FET amplifier.

Transcript

click the bell icon to get latest videos from ekeeda hello friends in this video we will start the ac analysis of fet amplifier we will start with common source mode of fft amplifier and here we go for ac analysis let's start so this is the circuit on the basis of which we will start our analysis this circuit is important for dc analysis so we'll m... Read More

Key Insights

• ℹ️ The common source mode of FET amplifiers involves connecting the input to the gate and the output to the drain, with the source as the common reference.
• 🔙 The AC analysis focuses on bypassed and unbypassed capacitor configurations, where the bypass capacitor simplifies the analysis by neglecting the source resistance.
• 🏡 The AC equivalent model of the FET amplifier uses the rpi model, which considers the transconductance (gm), output dynamic resistance (rd), and other rating parameters.
• ⚡ The voltage gain of the common source amplifier is calculated by applying KCL at node a and considering the parallel combination of the output resistances.
• 🟰 The input impedance of the amplifier is equal to the gate resistance (rg), while the output impedance is equal to the parallel combination of the output resistances (rd||rd).

Questions & Answers

Q: What is the common source mode of a FET amplifier?

In the common source mode, the input is connected to the gate terminal, the output is taken from the drain terminal, and the source is common for both the gate and drain. It is named as such because the reference voltage is at the source.

Q: How is the AC analysis different from the DC analysis?

In the AC analysis, the bypass capacitor is used to neglect the source resistance, allowing the source to be directly connected to ground. This simplifies the analysis by focusing only on AC voltages.

Q: How is the AC equivalent model of the FET amplifier constructed?

The AC equivalent model uses the rpi model, which is based on the transconductance (gm), output dynamic resistance (rd), and other rating parameters obtained from the FET transistor.

Q: How is the voltage gain calculated for the common source amplifier?

The voltage gain (vo/vi) is calculated by applying KCL at node a and considering the parallel combination of the output resistances. The formula for voltage gain is -gm(rd||rd).

Summary & Key Takeaways

• The video explains the common source mode of FET amplifiers and focuses on the AC analysis.

• The analysis is done on a specific circuit design, considering resistances, capacitances, and input voltage.

• The video covers both bypassed and unbypassed capacitor analysis and discusses the conversion of coupling capacitors.