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

MOSFET 𝑖 𝐷 = 1 2 𝑘 ′ 𝑛 𝑊 𝐿 𝑣 𝐺𝑆 − 𝑉 𝑡𝑛 2 (1+𝜆 𝑣 𝐷𝑆 ) 𝑖 𝐷 = 1 2 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 =

BJT

Collector current Base current Emitter current VT : the thermal potential β 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

Small-Signal Operation and Models 7.2.1 The MOSFET Case

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

Small-signal voltage gain

Modeling the Body effect

Collector current and Transcoductance If:

Equivalent circuit models

Configurations

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.

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)

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

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