1. Review for Final Exam MOSFET and BJT Basis of amplifiers
Obtaining linear amplification
Small-signal voltage Gain
Equivalent-circuit models: π model and T model
Basic configurations and Biasing
Analyze discrete-circuit amplifiers

2. MOSFET 𝑖 𝐷 = 1 2 𝑘 ′ 𝑛 𝑊 𝐿 𝑣 𝐺𝑆 − 𝑉 𝑡𝑛 2 (1+𝜆 𝑣 𝐷𝑆 )
𝑖 𝐷 = 𝑘 ′ 𝑛 𝑊 𝐿 𝑣 𝐺𝑆 − 𝑉 𝑡𝑛 2 (1+𝜆 𝑣 𝐷𝑆 )
𝑟 𝑜 = 𝑑 𝑖 𝐷 𝑑 𝑣 𝐷𝑆 −1 𝑤𝑖𝑡ℎ 𝑣 𝐺𝑆 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
𝑟 𝑜 = 𝑉 𝐴 𝐼 ′ 𝐷
𝐼 ′ 𝐷 =

4. BJT

5. Collector current Base current Emitter current
VT : the thermal potential
β is common-emitter current gain

6. Minority-Carrier Distribution

7. Equivalent Circuit Models

9. 6.3 BJT Circuit at DC
Use simple model: |VBE|=0.7V for a conducting transistor
and |VCE|=0.2V for a saturated transistor
Accurate model will increase complexity and impede insight in design
SPICE simulation in the final stage of design

10. Basis of amplifiers

11. 7.1.3 The voltage-transfer characteristics
VTC is non-linear:
For BJT:

12. Obtaining Linear Amplification by Biasing the Transistor
A dc voltage VGS is selected to obtain operation at a point Q on the segment AB of the VTC
Q: bias point or dc operation point, or quiescent point
The signal to be amplified is vgs(t)

13. Example 7.1
Solution: VGS=0.6V, VOV=0.2V

14. Small-Signal Operation and Models
7.2.1 The MOSFET Case

15. The signal current in the drain terminal
Small-signal condition:

16. Small-signal voltage gain

17. Modeling the Body effect

18. Collector current and Transcoductance
If:

19. Equivalent circuit models

21. Configurations

22. 7.4 Biasing
To establish in the drain (collector) a dc current that is predictable, and insensitive to variations in temperature and to large variations in parameter values between devices of the same type;
To locate the dc operating point in the active region and allow required output signal swing without the transistor leaving the active region.

23. Biasing The MOSFET case
- E.g., biasing by fixing VG and connecting a Rs

24. Example 7.11
Solution: design the resistance by distributing VDD into 3 equal part on RD, transistor VDS and RS
(each part = 5 V)

25. 7.5 Discrete-Circuit Amplifiers (self-reading)
A. A common-source (CS) amplifier

26. C. A CE amplifier with an emitter resistance Re With Re must use T Model