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Analog ElectronicsDifferential Amplifiers

The principal purpose of a constant-current source in the tail of a BJT differential pair is to?

  • AImprove bias stability and common-mode rejection
  • BMake both transistors permanently saturated
  • CReduce input resistance to zero
  • DRectify the input signal
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Correct Answer: A. Improve bias stability and common-mode rejection
Explanation: A high-resistance tail current source keeps the total emitter current nearly constant, improving differential operation and common-mode rejection.
Reference: Standard analog electronics: differential amplifiers
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