Neamen Microelectronics Chapter 4-1 Microelectronics Circuit Analysis and Design Donald A. Neamen Chapter 4 Basic FET Amplifiers
Neamen Microelectronics Chapter 4-2 In this chapter, we will: Investigate a single-transistor circuit that can amplify a small, time-varying input signal Develop small-signal models that are used in the analysis of linear amplifiers. Discuss and compare the three basic transistor amplifier configurations. Analyze the common-source amplifier. Analyze the source-follower amplifier. Analyze the common-gate amplifier. Analyze multitransistor or multistage amplifiers. Design a two-stage MOSFET amplifier circuit.
NMOS Common-Source Circuit Neamen Microelectronics Chapter 4-3
Neamen Microelectronics Chapter 4-4 NMOS Transistor Small-Signal Parameters Values depends on Q-point 1 1 2 1 ] [ ] ) ( [ ) ( 2 ) ( 2 DQ TN GSQ n o v i o DQ n TN GSQ n m gs d v i m I V V K r r I K V V K g v i g DS D GS D
Simple NMOS Small-Signal Equivalent Circuit Neamen Microelectronics Chapter 4-5
Neamen Microelectronics Chapter 4-6 NMOS Common-Source Circuit AC Small-signal A v V o V i g m ( r D) o
Problem-Solving Technique: MOSFET AC Analysis 1. Analyze circuit with only the dc sources to find quiescent solution. Transistor must be biased in saturation region for linear amplifier. 2. eplace elements with small-signal model. 3. Analyze small-signal equivalent circuit, setting dc sources to zero, to produce the circuit to the time-varying input signals only. Neamen Microelectronics Chapter 4-7
Common-Source Configuration DC analysis: Coupling capacitor is assumed to be open. AC analysis: Coupling capacitor is assumed to be a short. DC voltage supply is set to zero volts. Neamen Microelectronics Chapter 4-8
Neamen Microelectronics Chapter 4-9 Small-Signal Equivalent Circuit A v V o V i g m ( r o D )( i i Si )
Neamen Microelectronics Chapter 4-10 DC Load Line Q-point near the middle of the saturation region for maximum symmetrical output voltage swing,. Small AC input signal for output response to be linear.
Common-Source Amplifier with Source esistor Neamen Microelectronics Chapter 4-11
Neamen Microelectronics Chapter 4-12 Small-Signal Equivalent Circuit for Common-Source with Source esistor A v g 1 g m m D S
Neamen Microelectronics Chapter 4-13 Common-Source Amplifier with Bypass Capacitor Small-signal equivalent circuit
NMOS Source-Follower or Common Drain Amplifier Neamen Microelectronics Chapter 4-14
Neamen Microelectronics Chapter 4-15 Small-Signal Equivalent Circuit for Source Follower A v ( S o i 1 S ro i Si m g r )
Determining Output Impedance NMOS Source Follower O 1 g m S r o Neamen Microelectronics Chapter 4-16
Common-Gate Circuit Neamen Microelectronics Chapter 4-17
Neamen Microelectronics Chapter 4-18 Small-Signal Equivalent Circuit for Common Gate A v g ( m D L ) 1 g m Si A i I I O i ( D D L )( 1 g m g m Si Si )
Neamen Microelectronics Chapter 4-19 Comparison of 3 Basic Amplifiers Configuration Voltage Gain Current Gain Input esistance Output esistance Common Source A v > 1 TH Moderate to high Source Follower A v 1 TH Low Common Gate A v > 1 A i 1 Low Moderate to high
NMOS Amplifier with Enhancement Load Device Neamen Microelectronics Chapter 4-20
Cascade Circuit Neamen Microelectronics Chapter 4-21
Small-Signal Equivalent Circuit for Cascade Circuit Neamen Microelectronics Chapter 4-22