IV. Transistors (Biasing & Small-Signal Model) 4.1 Introduction Ampliﬁers are the main component of any analog circuit. Not only they can amplify the signal, they can be conﬁgured into may other useful circuits with a proper “feedback” (you will see this in 100 for OpAmps). In this course, we focus on simple transistor ampliﬁers. Joined Jun 1, 2002 Messages 2,014 Helped 507 Reputation 1,016 Reaction score 407 Trophy points 1,363 Activity points 14,195
Because the transistor has finite gain, you can't use very large resistors—such as something in the megaohm range—to bias the base. If you do, the emitter will pull down the voltage. One common addition to an audio amplifier is to bypass the emitter resistor with an electrolytic capacitor.
28 -6: Transistor Biasing For a transistor to function properly as an amplifier, an external dc supply voltage must be applied to produce the desired collector current. Bias is defined as a control voltage or current. Transistors must be biased correctly to produce the desired circuit voltages and currents.