Hybrid-pi model: Difference between revisions

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==BJT parameters==

The hybrid-pi model is a linearized [[two-port network]] approximation to the BJT using the small-signal base-emitter voltage, <math>\scriptstyle v_\text{be}</math>, and collector-emitter voltage, <math>\scriptstyle v_\text{ce}</math>, as independent variables, and the small-signal base current, <math>\scriptstyle i_\text{b}</math>, and collector current, <math>\scriptstyle i_\text{c}</math>, as dependent variables.<ref name=Jaeger1>

{{cite book

|author=R.C. Jaeger and T.N. Blalock

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|url=http://worldcat.org/isbn/0072320990

}}</ref> where:

* <math>\scriptstyle I_\text{C} \,</math> is the [[Quiescentquiescent current|quiescent]] collector current (also called the collector bias or DC collector current)

* <math>\scriptstyle V_\text{T} ~=~ \frac{kT}{e}</math> is the ''[[Boltzmann constant#Role in semiconductor physics: the thermal voltage|thermal voltage]]'', calculated from [[Boltzmann's constant]], <math>\scriptstyle k</math>, the [[elementary charge|charge of an electron]], <math>\scriptstyle e</math>, and the transistor temperature in [[kelvin]]s, <math>\scriptstyle T</math>. At approximately [[room temperature]] (295{{space}}K, 22{{space}}°C or 71{{space}}°F), <math>\scriptstyle V_\text{T}</math> is about 25 mV.

:<math>r_{\pi} = \left.\frac{v_\text{be}}{i_\text{b}}\right\vert_{v_\text{ce} = 0} = \frac{\beta_0}{g_m} = \frac{V_\text{T}}{I_\text{B}} \,</math> in [[Ohm (unit)|ohms]]