- Why is emitter bias more stable than base bias?
Emitter bias is more stable than base bias because it involves biasing the emitter terminal of the transistor to a fixed voltage, while the base-to-emitter voltage is varied. This method provides negative feedback that stabilizes the operating point of the transistor, making it less sensitive to variations in temperature and other parameters.
- Explain why the base bias Q-point changes with temperature.
One factor is the change in the base-to-emitter junction voltage (Vbe) with temperature. Vbe is a temperature-sensitive parameter that changes with temperature and is proportional to the bandgap voltage of the semiconductor material used to make the BJT. As temperature increases, Vbe decreases, which results in a change in the DC operating point (Q-point) of the transistor. Another factor is the change in the forward beta (β) of the transistor with temperature. β is the current gain of the transistor, which decreases with temperature due to a reduction in the doping level in the base region of the transistor. This reduction in β leads to a change in the current gain of the transistor and, as a result, changes the Q-point.
- How does emitter-feedback bias improve on base bias?
Emitter-feedback bias improves upon base bias by providing more stability to the operating point of a bipolar junction transistor. The emitter-feedback bias configuration involves connecting a resistor between the emitter and the base of the transistor.