# Review for Final Exam MOSFET and BJT Basis Review for Final Exam

MOSFET and BJT Basis of amplifiers Obtaining linear amplification

Small-signal voltage Gain Equivalent-circuit models: model and T model Basic configurations and Biasing Analyze discrete-circuit amplifiers MOSFET

1 2 = h ) (1+ ) ( 2

( ) =

[ ] 1

hh hh = BJT

Collector current Base current Emitter current

VT : the thermal potential is common-emitter current gain Minority-Carrier Distribution

Equivalent Circuit Models 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 Basis of amplifiers

7.1.3 The voltage-transfer characteristics VTC is non-linear: For BJT: 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) Example 7.1 Solution: VGS=0.6V, VOV=0.2V

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

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

Small-signal voltage gain Modeling the Body effect 17

Collector current and Transcoductance If: 18 Equivalent

circuit models 19 20

Configurations 7.4 Biasing 1. 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; 2. To locate the dc operating point in the active region and allow required output signal swing without the transistor leaving the

active region. 22 Biasing The MOSFET case

- E.g., biasing by fixing VG and connecting a Rs Example 7.11 Solution: design the resistance by distributing VDD into 3 equal part on RD, transistor VDS and RS

(each part = 5 V) 24 7.5 Discrete-Circuit Amplifiers (self-reading) A. A common-source (CS) amplifier

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

26