Reading from Chapter 4

Bipolar Junction Transistor

• An npn BJT has two layers of n-type material, known as the collector and emitter, and in between a layer of p-type material, known as the base.
• In order for a BJT to have a good performance, the base current needs to be small compared to the collector current.

$\beta =i_{C}/i_{D}$

• Operation in the active region:

*The base-emitter junction is forward biased.
*The base-collector junction is reverse biased.

• As amplifiers, BJTs operate in the active region.
• As switches, BJTs operate in saturation and cutoff.

Steps to analyze large signal dc models for BJT

1. Assume an operating region for the BJT like saturation, cutoff or active.
2. Solve the circuit to find $I_{C},I_{D},andV_{C}E$
3. Check to see if the values found in Step 2 are consistent with the assumed operating state. If    so the solution is complete; otherwise return to Step 1.