Field Effect Transistor Biasing and Configuration It provides the simplest configuration in understanding the FET. In this slide, it's only described and elaborate the Basic Current Relationship of FET.

1. FET
Biasing
Engr. Jesus Rangcasajo
ECE 321 Instructor
jesusrangcasajo@gmail.com

2. Basic Current Relationships
Things to ponder!

3. Fixed-Bias Configuration
𝑰 𝑮 ≅ 𝟎𝑨
𝑉𝑅𝑔 = 𝐼 𝐺 𝑅 𝐺 = 0 = 𝑅 𝐺0𝑉
The zero volt drop across 𝑅 𝐺
permits replacing 𝑅 𝐺 by a short
circuit equivalent.

4. 1
@ loop 1:
𝑽 𝑮𝑺 = −𝑽 𝑮𝑮
−𝑉𝐺𝐺 − 𝑉𝐺𝑆 = 0
2
@ loop 2:
𝑉𝐷𝐷 − 𝐼 𝐷 𝑅 𝐷 − 𝑉𝐷𝑆 − 𝑉𝑆 = 0
𝑽 𝑫𝑺 = 𝑽 𝑫𝑫 − 𝑰 𝑫 𝑹 𝑫𝑉𝑆 = 0
Using Double subscript notation:
𝑉𝐷𝑆 = 𝑉𝐷 − 𝑉𝑠
𝑉𝐷𝑆 = 𝑉𝐷
𝑉𝐺𝑆 = 𝑉𝐺 − 𝑉𝑠
𝑉𝐺𝑆 = 𝑉𝐺

5. For
Example: Find:

6. Self-Bias Configuration

7. 1
@ loop 1:
−𝑉𝐺𝑆 − 𝑉𝑅𝑠 = 0
𝑽 𝑮𝑺 = −𝑽 𝑹𝒔 = −𝐼 𝐷 𝑅 𝑠
Note that the
current through 𝑅 𝑠
is the source
current, 𝐼𝑆
But
𝐼 𝐷 = 𝐼𝑆
𝑉𝑅𝑠 = 𝐼 𝐷 𝑅 𝑠

8. 𝑉𝐷 = 𝑉𝐷𝐷 − 𝑉𝑅𝐷

9. Self-Bias Configuration –
graphical solution
1. Sketch the transfer curve
2. Draw the line
𝑽 𝑮𝑺= −𝐼 𝐷 𝑅 𝑠
3. The Q-point is located where the
line intersects the transfer curve.
Shorthand
Method:
𝐼 𝐷 =
𝐼 𝐷𝑆𝑆
4
𝑉𝐺𝑆 =
𝑉𝑝
2

11. Voltage-Divider Bias

12. Using voltage divider, you get the
value of 𝑉𝐺

17. For Example:

18. Source:
Electronic Devices and Circuit
Theory, 10th Ed., R. Boylestad &
L. Nashelsky, Copyright ©2009
by PEARSON Education, Inc.