Common-Mode Rejection Ratio of MOS with Current-Mirror Load Calculator

Formula Used:

\[ CMRR = g_m \times \left( \frac{1}{\frac{1}{R'_1} + \frac{1}{R'_2}} \right) \times (2 \times \Delta g_m \times R_{fo}) \]

Transconductance (g_m):

Primary Winding Resistance in Secondary (R'_1):

Secondary Winding Resistance in Primary (R'_2):

Change in Transconductance (Δg_m):

Finite Output Resistance (R_fo):

Common Mode Rejection Ratio (CMRR):

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1. What is Common-Mode Rejection Ratio?

Common Mode Rejection Ratio 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.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ CMRR = g_m \times \left( \frac{1}{\frac{1}{R'_1} + \frac{1}{R'_2}} \right) \times (2 \times \Delta g_m \times R_{fo}) \]

Where:

\( g_m \) — Transconductance (S)
\( R'_1 \) — Primary Winding Resistance in Secondary (Ω)
\( R'_2 \) — Secondary Winding Resistance in Primary (Ω)
\( \Delta g_m \) — Change in Transconductance (S)
\( R_{fo} \) — Finite Output Resistance (Ω)

Explanation: The formula calculates the ability of a MOS circuit with current-mirror load to reject common-mode signals.

3. Importance of CMRR Calculation

Details: High CMRR is crucial for differential amplifiers as it indicates better rejection of common-mode noise and interference, leading to cleaner signal processing.

4. Using the Calculator

Tips: Enter all values in appropriate units (Siemens for transconductance, Ohms for resistance). All values must be positive and non-zero.

5. Frequently Asked Questions (FAQ)

Q1: What is a good CMRR value?
A: Higher CMRR values are better. Typically, values above 80-100 dB are considered good for most applications.

Q2: Why is CMRR important in differential amplifiers?
A: CMRR determines how well the amplifier can reject common-mode noise while amplifying the differential signal.

Q3: What factors affect CMRR?
A: Component matching, transistor characteristics, and circuit symmetry all affect the CMRR of an amplifier.

Q4: How can CMRR be improved?
A: Using matched components, increasing circuit symmetry, and employing current-mirror loads can improve CMRR.

Q5: What are typical applications of high CMRR amplifiers?
A: Medical instrumentation, audio equipment, and communication systems where noise rejection is critical.