Output Resistance of CS Amplifier with Source Resistance Calculator

Formula Used:

\[ R_d = R_{out} + R_{so} + (g_{mp} \times R_{out} \times R_{so}) \]

Finite Output Resistance (R_out):

Source Resistance (R_so):

MOSFET Primary Transconductance (g_mp):

Drain Resistance (R_d):

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1. What is the Output Resistance of CS Amplifier with Source Resistance?

The output resistance of a common source (CS) amplifier with source resistance is a key parameter that determines the amplifier's ability to drive loads and maintain signal integrity. It represents the resistance seen at the drain terminal when looking into the output.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ R_d = R_{out} + R_{so} + (g_{mp} \times R_{out} \times R_{so}) \]

Where:

\( R_d \) — Drain Resistance (Ω)
\( R_{out} \) — Finite Output Resistance (Ω)
\( R_{so} \) — Source Resistance (Ω)
\( g_{mp} \) — MOSFET Primary Transconductance (S)

Explanation: The formula accounts for the combined effect of the finite output resistance, source resistance, and the amplification factor provided by the MOSFET's transconductance.

3. Importance of Drain Resistance Calculation

Details: Accurate calculation of drain resistance is crucial for designing amplifier circuits with proper impedance matching, maximizing power transfer, and ensuring stable operation across different load conditions.

4. Using the Calculator

Tips: Enter finite output resistance and source resistance in ohms (Ω), and MOSFET primary transconductance in siemens (S). All values must be positive numbers greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: Why is source resistance important in CS amplifier design?
A: Source resistance affects the overall gain, linearity, and output impedance of the amplifier. It provides negative feedback that stabilizes the amplifier's operation.

Q2: How does MOSFET transconductance affect the output resistance?
A: Higher transconductance increases the effective output resistance due to the amplification effect in the feedback path, making the amplifier more ideal for voltage amplification.

Q3: What are typical values for these parameters?
A: Output resistance typically ranges from kΩ to MΩ, source resistance from Ω to kΩ, and transconductance from mS to hundreds of mS depending on the MOSFET size and bias conditions.

Q4: When should this calculation be used?
A: This calculation is essential when designing common source amplifiers for audio applications, RF circuits, and any application where impedance matching and signal integrity are critical.

Q5: Are there limitations to this formula?
A: This formula assumes small-signal operation and may not account for all non-ideal effects in real MOSFETs, such as channel length modulation at very high frequencies.