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ECE523/421 - Lecture 3 Slide: 1University of New Mexico
Office: ECE Bldg. 230BOffice hours: Tuesday 2:00-3:00PM or by appointment
E-mail: [email protected]
Payman Zarkesh-Ha
ECE 523/421 – Analog Electronics
Lecture 3: Basic MOSFET Amplifiers II
ECE523/421 - Lecture 3 Slide: 2University of New Mexico
Review of Last Lecture MOSFET Biasing for Amplification
MOSFET Small Signal (Π and T Models)
Basic MOSFET Amplifier Configurations (CS, CG, CD)
Examples
ECE523/421 - Lecture 3 Slide: 3University of New Mexico
Today’s Lecture Biasing in MOS Amplifier Circuits
• Fix VGS Biasing
• Fix VGS Biasing with Source Resistance
• Drain-to-Gate Feedback Resistor Biasing
• Constant Current Source Biasing
Role of Body Effect in MOS Amplifiers
Temperature Effect
ECE523/421 - Lecture 3 Slide: 4University of New Mexico
Problem of Fix VGS Biasing
ECE523/421 - Lecture 3 Slide: 5University of New Mexico
Advantage of RS in Fix VGS Biasing
ECE523/421 - Lecture 3 Slide: 6University of New Mexico
Example: Bias Circuit Design I
1) Design the following circuit to operate at a dc drain current of 0.5 mA and VD = +2 V. Let Vt= 1V , K’nW/ L = 1 mA/V2, and λ=0, VDD=VSS=5 V. Use standard 5% resistor values and give the resulting values of ID, VD, and VS.
ECE523/421 - Lecture 3 Slide: 7University of New Mexico
Drain-to-Gate Feedback Biasing
ECE523/421 - Lecture 3 Slide: 8University of New Mexico
Constant Current Source Biasing
ECE523/421 - Lecture 3 Slide: 9University of New Mexico
Using two transistors Q1 and Q2 having equal lengths but widths related by W2/W1=5, design the current mirror circuit to obtain I=0.5mA. Let VDD=-VSS=5V, K’n(W/L)1=0.8mA/V2, Vt=1V, and λ=0. Find the required value for R. What is the voltage at eth gate of Q1 and Q2? What is the lowest voltage allowed at the drain of Q2 while Q2 remains in the saturation region?
Example: Bias Circuit Design II
ECE523/421 - Lecture 3 Slide: 10University of New Mexico
Review of Common-Source Amplifier
ECE523/421 - Lecture 3 Slide: 11University of New Mexico
Review of Common-Gate Amplifier
ECE523/421 - Lecture 3 Slide: 12University of New Mexico
Review of Source Follower Circuit
ECE523/421 - Lecture 3 Slide: 13University of New Mexico
Quick Review of Frequency Response
ECE523/421 - Lecture 3 Slide: 14University of New Mexico
Modeling of Body Effect
mmb gg
SBf V22
ECE523/421 - Lecture 3 Slide: 15University of New Mexico
Temperature Effect Vt increases by about 2mV/ºC by temperature increase
K’n decreases more by temperature increase
Overall ID decreases as temperature increase
This is an advantage for MOSFET devices (No thermal runaway)