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other bjt amplifiers

Common Collector (CC) Amplifier. A CC amplifier provides current and power gain.CC input and output signal voltages are in phase.A CC amplifier is also referred to as an emitter follower.. Emitter Follower DC Relationships. Example 10.1Example 10.2 p364-365. FIGURE 10.4 . AC Equivalent Circuit.

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other bjt amplifiers

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    1: Other BJT Amplifiers

    3: Emitter Follower DC Relationships

    5: FIGURE 10.4

    6: AC Equivalent Circuit The ac equivalent of the emitter follower shows that the output signal voltage is developed across rE. rE = RE || RL

    7: Emitter Follower Gain Circuit current gain is significantly lower than the transistor hfe rating. Voltage gain is less than unity (1). Av is assumed to be approximately equal to 1 when rE >> r’e . Ap < Ai because Av < 1.

    8: Emitter Follower Impedances Input impedance is relatively high; higher than that of a comparable CE amplifier. The value of hfc is equal to (hfe + 1). In most cases, we assume that hfc ? hfe. Output impedance is relatively low; lower than that of a comparable CE amplifier.

    9: Using Emitter-Feedback Bias Emitter followers are often emitter-feedback biased to provide higher amplifier input impedance.

    10: Decoupling Capacitor Decoupling capacitor – A capacitor connected between VCC and ground, in parallel with the dc power supply. Used to prevent emitter-follower output distortion (shown in the lower of the two waveforms). A regulated dc power supply can also be used to prevent this distortion.

    11: Emitter follower application

    12: Buffers

    13: Darlington Pair Darlington pair – A pair of transistors connected to provide higher current gain and input impedance than a single transistor.

    14: Darlington Emitter Follower

    15: Darlington Emitter Follower

    16: Common Base (CB) Amplifiers A CB amplifier provides voltage and power gain. CB input and output signal voltages are in phase.

    17: CB Amplifier AC Analysis

    18: CB Amplifier Buffer The CB amplifier can be used to couple a low-impedance voltage source to a higher-impedance load.

    19: High-Frequency Characteristics The ground at the base terminal results in relatively high stability. Changes in the output circuit have little effect on the input circuit. CB amplifiers generate little noise. Noise – Any undesired voltage or current generated within, or externally to, an electronic system. Noise has natural and man-made sources. High frequency, low-amplitude signals are highly susceptible to noise.

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