Common-Mode Rejection Ratio Of MOSFET In Decibels Calculator

Common-Mode Rejection Ratio Formula:

\[ CMRR_{db} = |20 \times \log_{10}\left(\frac{A_v}{A_{cm(db)}}\right)| \]

Common-Mode Rejection Ratio (CMRR_db):

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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, particularly differential amplifiers, to reject common-mode signals. These are signals that appear simultaneously and in-phase on both input terminals of the circuit.

2. How Does the Calculator Work?

The calculator uses the CMRR formula:

\[ CMRR_{db} = |20 \times \log_{10}\left(\frac{A_v}{A_{cm(db)}}\right)| \]

Where:

\( A_v \) — Voltage gain of the differential amplifier (dB)
\( A_{cm(db)} \) — Common mode gain of the amplifier (dB)
\( \log_{10} \) — Base-10 logarithm function
\( | | \) — Absolute value function

Explanation: The formula calculates the ratio of differential gain to common-mode gain in decibels, providing a measure of how effectively the circuit rejects common-mode signals.

3. Importance of CMRR Calculation

Details: CMRR is a critical parameter in differential amplifiers and instrumentation systems. A high CMRR indicates better rejection of common-mode noise and interference, which is essential for accurate signal processing in noisy environments.

4. Using the Calculator

Tips: Enter the voltage gain and common mode gain values in decibels. Both values must be positive numbers greater than zero for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is considered a good CMRR value?
A: Higher CMRR values are better. Typically, values above 80-100 dB are considered good, with professional instrumentation amplifiers achieving 120 dB or more.

Q2: Why is CMRR important in MOSFET circuits?
A: MOSFET-based differential amplifiers are widely used in integrated circuits. High CMRR ensures better noise immunity and signal integrity in these applications.

Q3: How does temperature affect CMRR?
A: Temperature variations can affect component matching in differential pairs, potentially reducing CMRR. Proper circuit design and temperature compensation are important.

Q4: Can CMRR be improved in circuit design?
A: Yes, through careful component matching, use of current sources, balanced circuit layouts, and dedicated instrumentation amplifier ICs.

Q5: What's the difference between CMRR and PSRR?
A: CMRR measures rejection of common-mode input signals, while PSRR (Power Supply Rejection Ratio) measures rejection of power supply noise and variations.