Content deleted Content added
Line 31:
:<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>
where:
* <math>\scriptstyle \beta_0 ~=~ \frac{I_\text{C}}{I_\text{B}} \,</math> is the current gain at low frequencies (generally quoted as ''h''<sub>''fe''</sub> from the [[Bipolar junction transistor#h-parameter model|h-parameter model]]). Here <math>\scriptstyle I_\text{B}</math> is the DC (bias) base current. This is a parameter specific to each transistor, and can be found on a datasheet.
* <math>\scriptstyle r_\text{O} ~=~ \left.\frac{v_\text{ce}}{i_\text{c}}\right\vert_{v_\text{be} = 0} ~=~ \frac{V_\text{A} \,+\, V_\text{CE}}{I_\text{C}} ~\approx~ \frac{V_\text{A}}{I_\text{C}}</math> is the output resistance due to the [[Early effect]] (<math>\scriptstyle V_\text{A}</math> is the Early voltage).
| |||