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The Reference Current in a BJT (Bipolar Junction Transistor) current mirror is a stable current source that determines the output current. It is calculated based on the collector current and the common emitter current gain of the transistor.
The calculator uses the formula:
Where:
Explanation: This formula accounts for the base currents in the current mirror configuration, providing an accurate reference current calculation.
Details: Accurate reference current calculation is crucial for designing stable current sources in analog circuits, ensuring proper biasing and consistent performance across temperature variations and process changes.
Tips: Enter collector current in amperes and common emitter current gain (β). Both values must be positive numbers for valid calculation.
Q1: What is a BJT current mirror?
A: A BJT current mirror is a circuit configuration that copies a current from one active device to another, maintaining a constant current flow regardless of loading.
Q2: Why is the 2/β term included in the formula?
A: The 2/β term accounts for the base currents of the two transistors in the basic current mirror configuration.
Q3: What are typical values for β in BJT transistors?
A: Common emitter current gain β typically ranges from 50 to 200 for most bipolar junction transistors, depending on the specific device and operating conditions.
Q4: When is this formula most accurate?
A: This formula provides good accuracy when the transistors are matched, operating in the active region, and when Early voltage effects are negligible.
Q5: Are there limitations to this current mirror configuration?
A: The basic current mirror has limited accuracy due to base current errors. More advanced configurations like Wilson current mirror or cascode current mirror provide better performance.