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DC operating point

A typical CE circuit is shown in the figure below, where $I_E=I_B+I_C$, $V_{in}=V_{BE}=V_B$, and $V_{out}=V_{CE}=V_C$.

transistorbiasingc.gif

The DC operating point (also known as bias point, quiescent point, or Q-point) is the DC steady-state operating condition of a transistor, (with no AC input signal applied), determined by $I_B$ and $V_{BE}$ of the input port, and $I_C$ and $V_{CE}$ of the output port.

From the current-voltage plot of the output characteristics, we see that the operation of a transistor can be in one of the three possible regions:

Example: In the CE circuit shown below, $V_{CC}=12V$, $R_B=6 K\Omega$, $R_C=2 K\Omega$, $\beta=60$. The load line can be determined by two points: $(V_{CE}=0,\;I_C=V_{CC}/R_C=6\;mA)$ and $(I_C=0,\;V_{CE}=V_{CC}=12\;V)$. Find output voltage $V_{out}=V_{CE}$ when $V_{in}$ takes the following values:

CEexample2.png


next up previous
Next: AC Signal Amplification Up: ch4 Previous: Bipolar Junction Transistor (BJT)
Ruye Wang 2014-11-26