1. Review & Problems

2. Modes of Operation BE Junction\BC Junction Forward Biased
Reverse Biased
Saturation
Active
Reverse Active Mode
Cut-Off
Applications:
1. Saturation and cut-off mode are used in digital circuits.
2. Active mode is used in the amplifier design.

3. Voltage and Current Polarities of NPN and PNP transistors
A “fat” voltage between collector and emitter voltage places a transistor in the active region!
A “skinny” voltage between collector and emitter voltage places a transistor in the active region!

4. BJT in the active mode
(NPN)
(PNP)
True for both PNP and NPN

5. Small Signal Equivalent Circuit for BJT in the active mode

6. Calculation of small signal parameters

7. Small Signal Model Observations:
Both Q1 and Q2 are represented by the SAME small signal circuit.
To find the output resistance, find the terminal resistance by applying
a test voltage.

8. Terminal Resistance Eq Eq Eq

9. Formula to Memorize

11. NPN to NMOS