Second Emitter Current of BJT Differential Amplifier Calculator

Formula Used:

\[ i_{E2} = \frac{i}{1 + e^{\frac{V_{id}}{V_{th}}}} \]

Second Emitter Current (iE2):

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1. What is the Second Emitter Current of BJT Differential Amplifier?

The Second Emitter Current in a BJT Differential Amplifier refers to the current flowing through the emitter of the second transistor in a differential pair configuration. This current distribution is crucial for understanding the amplifier's operation and gain characteristics.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ i_{E2} = \frac{i}{1 + e^{\frac{V_{id}}{V_{th}}}} \]

Where:

\( i_{E2} \) — Second Emitter Current (A)
\( i \) — Total current (A)
\( V_{id} \) — Differential Input Voltage (V)
\( V_{th} \) — Threshold Voltage (V)
\( e \) — Napier's constant (approximately 2.71828)

Explanation: This formula describes how the current divides between the two transistors in a differential pair based on the differential input voltage and threshold voltage.

3. Importance of Second Emitter Current Calculation

Details: Accurate calculation of the second emitter current is essential for analyzing differential amplifier performance, determining common-mode rejection ratio, and designing balanced amplifier circuits.

4. Using the Calculator

Tips: Enter the total current in amperes, differential input voltage in volts, and threshold voltage in volts. All values must be positive and valid.

5. Frequently Asked Questions (FAQ)

Q1: What is a BJT Differential Amplifier?
A: A BJT Differential Amplifier is a circuit that amplifies the difference between two input signals while rejecting signals common to both inputs.

Q2: Why is the current distribution important?
A: The current distribution between the two transistors determines the amplifier's gain, linearity, and common-mode rejection characteristics.

Q3: What is the typical range of threshold voltage?
A: For silicon BJTs, the threshold voltage is typically around 25-30 mV at room temperature.

Q4: How does temperature affect the calculation?
A: The threshold voltage Vth is temperature-dependent (Vth = kT/q), so temperature variations will affect the current distribution.

Q5: Can this formula be used for MOSFET differential pairs?
A: While similar in concept, MOSFET differential pairs use different equations due to their square-law characteristics rather than exponential.