Audio Engineering

Audio Amplifi ers 285

Ic

hfe

Ib

Figure 9.1 : BJT nonlinearity.

hfe

Frequency

Figure 9.2 : Decrease in hfe with frequency.

shown for an NPN silicon transistor as line ‘ a ’ in Figure 9.3. (I have included, as line
‘ b ’ , for reference, the comparable characteristics for a germanium junction transistor,
although this would normally be a PNP device with a negative base voltage, and a
negative collector voltage supply line.) By comparison with, say, a triode valve, whose
anode current/grid voltage relationships are also shown as line ‘ c ’ in Figure 9.3 , the BJT