Common-Mode Rejection Ratio Of MOSFET Given Resistance Calculator

Common-Mode Rejection Ratio Formula:

\[ CMRR = \frac{2 \times g_m \times R_{out}}{\frac{\Delta R_D}{R_d}} \]

Transconductance (gₘ):

Siemens

Output Resistance (Rₒᵤₜ):

Change in Drain Resistance (ΔR_D):

Drain Resistance (R_d):

Common-Mode Rejection Ratio (CMRR):

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1. What is Common-Mode Rejection Ratio?

The Common-Mode Rejection Ratio (CMRR) is a measure of the ability of an electronic circuit, such as an amplifier, to reject noise and interference that is common to both the input signals. It quantifies how well the circuit can amplify the differential signal while suppressing common-mode signals.

2. How Does the Calculator Work?

The calculator uses the CMRR formula for MOSFET circuits:

\[ CMRR = \frac{2 \times g_m \times R_{out}}{\frac{\Delta R_D}{R_d}} \]

Where:

\( g_m \) — Transconductance (Siemens)
\( R_{out} \) — Output Resistance (Ω)
\( \Delta R_D \) — Change in Drain Resistance (Ω)
\( R_d \) — Drain Resistance (Ω)

Explanation: The formula calculates how effectively a MOSFET differential amplifier rejects common-mode signals based on its transconductance, output resistance, and the mismatch in drain resistances.

3. Importance of CMRR in MOSFET Circuits

Details: High CMRR is crucial for differential amplifiers as it ensures that common-mode noise and interference are effectively rejected, resulting in cleaner signal amplification and better circuit performance in noisy environments.

4. Using the Calculator

Tips: Enter transconductance in Siemens, output resistance in ohms, change in drain resistance in ohms, and drain resistance in ohms. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a good CMRR value for MOSFET amplifiers?
A: Higher CMRR values are better. Typically, values above 60-80 dB are considered good, with professional audio applications requiring 100 dB or more.

Q2: How does drain resistance mismatch affect CMRR?
A: Mismatch in drain resistances directly reduces CMRR. The greater the mismatch (ΔR_D), the lower the CMRR, making the circuit more susceptible to common-mode noise.

Q3: What factors can improve CMRR in MOSFET circuits?
A: Using matched transistors, increasing output resistance, improving transconductance, and minimizing resistance mismatches can all help improve CMRR.

Q4: Why is CMRR important in instrumentation amplifiers?
A: Instrumentation amplifiers often operate in noisy environments where common-mode signals are prevalent. High CMRR ensures accurate measurement of small differential signals.

Q5: How does temperature affect CMRR?
A: Temperature changes can cause parameter variations in MOSFETs and resistors, potentially increasing mismatches and reducing CMRR over temperature ranges.