š Key Concepts
ā¢ How base bias voltage (VBB) sets the transistorās quiescent (no-signal) operating point
ā¢ Relationship between bias point and conduction angle (how much of the input sine wave the transistor conducts) for classes A, AB, B, and C
ā¢ Compare figure 4ās bias network with the other three figures to see if the transistor is biased well into conduction, just at cutoff, or well below cutoff
š Think About
ā¢ Look at where the base voltage is set in figure 4 relative to the emitter voltage. Is the base strongly forwardābiased, barely forwardābiased, or actually reverseābiased at no signal?
ā¢ Think about what that base condition means for how many degrees of the input sine wave will produce collector current: almost all of it, about half, slightly more than half, or less than half?
ā¢ Compare figure 4 to the classic textbook definitions of class A, class AB, class B, and class C in terms of conduction angle (360Ā°, >180Ā°ā<360Ā°, 180Ā°, or <180Ā°).
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Before You Answer
ā¢ Verify whether VBB in figure 4 makes the base more negative or more positive than in the other circuits
ā¢ Confirm whether the transistor in figure 4 is conducting at the quiescent point (no input signal) or is cut off until the input swings far enough
ā¢ Match that conduction behavior to the standard amplifier class definitions: Class A (360Ā°), Class AB (>180Ā°ā<360Ā°), Class B (180Ā°), Class C (<180Ā°)