This presentation shall give you a basic knowledge of how a BJT does the amplification of signals.

2. Overview
• General idea for amplifying a signal voltage source.
• Large signal characteristics of BJT.
• Various other parameters of BJT.
• Realization of the idea using a physical device
(which is our BJT).
• What would happen if we apply signals directly to
BJT?
• What would happen if we apply large signals?
• Concept of Shrink and Boost (Small Signal Model)
• Lets build a Common Base Amplifier (Current
Buffer)

3. • Convert the signal voltage source into a current
source and pass it through a resistor!
• In doing so we must ensure that Output Power is
greater than the Input Power.
 Input = Vs
 Output = Is x RL
 Gain = Output/Input = (Is x RL)/Vs
General idea for amplifying a signal voltage source.

4. You might be thinking…..
How to Implement this idea?
How do we convert a voltage into a current?
Try a resistor!
Yeah, we have succeeded in converting a voltage into current 

5. Now, how to pass this current through a resistor to get
amplification?
Hmm…
𝑉𝑜 = 𝑉𝑠 ×
𝑅𝐿
𝑅𝐿 + 𝑅
𝐼 =
𝑉𝑠
(𝑅 𝐿 + 𝑅)
Vo Vo < Vs
Po < Pi
Current I, has also
Decreased.
Output Power,
Po = I x 𝑅_
Input Power,
Pi = I x Vs
This surely doesn’t work


6. Vo

9. Here is the Solution!! 

10. Large signal characteristics of BJT.

12. PNP Transistor in Unbiased Condition

13. Widening of C-B Depletion Layer &
Narrowing of E-B Depletion Layer

14. Electron-Hole Recombination at Base
& Emitter holes pushed into C-B Depletion Layer

15. Amplification!!! 

16. And this process continues.. (1)

17. And this process continues.. (2)

18. And this process continues.. (3)

19. Most Interesting Part of the Whole PPT
R

20. Realization of the Idea

21. 2 Questions.
1. What would happen if we apply signals directly to BJT?
2. What would happen if we apply large signals?

22. Concept of Shrink and Boost (Small Signal Model)
Input Operating Point

23. Output Operating Point

24. Complete Large Signal Model

25. Adding Signal Source to the Large Signal Model
Vo

26. Common Base Amplifier (Current Buffer)

27. Thank You 