Temperature Dependance of the BJT Small-Signal Model

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SMALL SIGNAL MODEL FOR THE BJT

\boldsymbol{i_C} is the total current. \boldsymbol{I_C} is the DC biasing current. \boldsymbol{i_c} is the small signal current (lowercase letter i with subscript lowercase letter c). If we can find a representation for it, it can be used for the model.

What comes next is very surprising and important! Have you ever noticed that for {g_m V_{be}} , which is {\frac{I_c} {V_t} V_{be}}, which is the small signal model for {i_{c}}, to be a viable model, your {V_{be}} would have to be sufficiently smaller than the thermal voltage at room temperature?? I didn’t, either! This is outstanding!

For the neglection of higher order terms to work, your {V_{be}} needs to be sufficiently smaller than your {V_{t}}, and {V_{be}} is 50mV at room temperature.

Now this, is a proper definition of a small signal for the BJT!

Published by giiray

Writing for G&C Bards, a project that collects and connects stories and those who tell them.

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