Common base
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- This article is about a concept in electronic circuits. For the philosophical concept, please see Common base (Unification Thought).
Common_base.png
In electronics, common base refers to a type of bipolar transistor circuit in which a transistor is connected such that its base terminal is wired to the 0 volt or "common" rail of the circuit (or can be considered so for AC signals). This arrangement is relatively uncommon, but is occasionally employed for amplifiers that require an unusually low input impedance, or for VHF and UHF amplifiers where the fact that the output circuit only passes through a single PN junction rather than the two junctions of a common emitter amplifier gives a crucial advantage.
Characteristics
Inherent voltage gain:
- With CE:
- <math>
g_m (R_C || R_{load}) <math>
Input resistance:
- <math>
R_E || {r_\pi \over 1 + \beta_0} <math>
Current gain:
- <math>
A_{vm} {r_{in} \over R_{load}} <math>
Output resistance:
- <math>
R_C <math>