Common Base Biasing Circuits

Figure below shows the circuit diagram of common-base configuration. Here, the input is applied to the emitter terminal and the output is taken from the collector terminal. The base terminal is common to both the input and the output sections.

Common-base configuration

Figure below shows the DC equivalent circuit of common-base configuration. Applying Kirchhoff’s voltage law to the input section (emitter–base loop), we get

Therefore, the emitter current (I_E) is equal to

DC equivalent of common-base circuit

Applying Kirchhoff’s voltage law to the output section (collector–emitter loop), we get

Therefore,

The operating point for the common-base configuration is given by

The load line is drawn using the output equation given by

Substituting I_C = 0, we get

Substituting V_CB = 0, we get

Joining the two points we can draw the DC load line on the output characteristics as shown in figure below. The operating point (I_CQ, V_CBQ) is determined by the point of intersection of the load line with the characteristic curves at the value of emitter current (I_E).

Load-line analysis of common-base configuration