In load-line analysis of a transistor amplifier, what determines the Q-point?

• A. The slope of the AC gain curve.
• B. The maximum collector current achieved at zero load.
• C. The intersection of the DC load line with the transistor’s Ic-Vce characteristics.
• D. The frequency response of the amplifier.

Answer: (C)

In load-line analysis, the DC operating point is found where the transistor’s Ic–Vce characteristics intersect the circuit’s DC load line. The DC load line represents the relationship between Ic and Vce imposed by the biasing network and supply, for a simple common-emitter with a collector resistor this is Vce = Vcc − Ic Rc. The Q-point is exactly that intersection, and it fixes both Ic and Vce for the transistor when there’s no input signal. This point should lie in the active region to allow symmetrical swing of the output around it.

The slope of the AC gain curve, the maximum collector current at zero load, and the frequency response describe different aspects (small-signal gain, DC bias limits, and dynamic behavior, respectively) and do not determine the DC operating point.