Physics · Ch 9 — Semiconductor Electronics
Common-Base (CB) Configuration
Common-Base (CB) Configuration
In the common-base configuration, the BASE terminal is common to both the input and the output circuit loop. The input current is the emitter current (the input signal is applied between emitter and base), and the output current is the collector current (the output is measured between collector and base) -- base itself is simply the shared reference terminal for both loops. Because the base is common to both loops here, the common-base current gain (9.4.3.4) is the natural figure of merit for this configuration, and since (the base current being so small), common base offers a voltage gain but a current gain always just under 1 -- useful in high-f …
What this figure shows. Panel (a) draws the schematic circuit: an NPN transistor (N-P-N regions labelled) with a bias source connected between emitter and the (common) base, driving input current , and a second bias source connected between collector and the same common base, with output current and base current also marked flowing into/out of the base terminal. Panel (b) redraws the identical circuit using the transistor's standard circuit symbol in place of the labelled N-P-N block, making explicit that in this configuration BOTH (input loop) and (output loop) share the base as …