Bipolar Junction Transistors can be connected in three major configurations. The following schematic is for the most used of these configurations.
R1 Set bias
R2 Set bias & develop input
R3 Develop the output
R4 Prevent Degeneration
C1 Coupling Capacitors to separate the AC signals from the DC biasing voltage.
C2 Coupling Capacitors to separate the AC signals from the DC biasing voltage.
C3 Bypass Capacitor
Q1 2N2904 NPN BJT
Common Emitter Characteristics
The main characteristics of importance are input impedance, gain, and output impedance. Other important characteristics are input and output phase relationship and frequency response. The impedance is indicated in ohms, the phase in degrees and the gain as beta DC or HFE.
input impedance Medium
Output impedance Medium
Voltage gain Medium
Current gain Medium
Power gain High
Input/Output phase 180°
Common Emitter Application
Applications include amplifier, phase inverter, switch and much much more.
The other two basic configurations are the common base and common collector (emitter follower) configurations. They provide a variety of options in impedance, phase. and gain characteristics. These two configurations will be covered in future posts