Chapter Summary

This chapter explained how a bipolar junction transistor is set up for use. An unbiased transistor is of no practical use; applying a suitable DC voltage — transistor biasing — fixes the DC currents and voltages and places the device in the required region. The DC load line, drawn between the saturation point $I_{C(sat)} = V_{CC}/R_C$ and the cutoff point $V_{CE(cutoff)} = V_{CC}$, holds every possible operating point, and the Q point (operating/quiescent point) is where the load line meets the output characteristic for zero signal. For switching the Q point is placed in saturation or cutoff; for faithful amplification it is placed at the centre of the active region. Among the biasing methods, voltage divider (universal) bias is preferred because its Q point is almost independent of $\beta$, giving excellent stabilisation through the emitter resistor $R_E$. The chapter also covered the leakage currents $I_{CBO}$ and $I_{CEO}$ ( …