上海交大模电讲稿05.ppt

Basic Theory of Circuits, SJTU Chapter 5 Operational Amplifier Introduction Terminal Voltage and Currents Ideal op amp Applications Applications * * A typical op amp: a) pin configuration, b) circuit symbol An op amp is an active circuit element designed to perform mathematical operation of addition, subtraction, multiplication, division, differentiation, and integration. Vd=V2-V1 (differencial input) Vo=AVd=A(V2-V1) A: gain (open-loop voltage gain) Actual op amp: Ri(very large); Ro(very small); A(very large) Idealization: Ri=? ; Ro=0 ; A= ? As Vo is limited, we can get from Vo=A(V2-V1) that: V2=V1 As Ri= ?, we can get i1=0, i2=0 i1 i2 i1=0 , i2=0 ; V1=V2 Ideal op amp model i1 i2 Inverting Amplifier Noninverting amplifier If Rf=0; R1=?, then= The voltage follower Vi Vo + - + - First stage Second stage Applications Summing amplifier Applications Difference Amplifier 2 1 3 2 3 4 1 a b Note: be careful while using nodal analysis, do not set nodal equation at the output terminal. Example: Find out Vo R6 R5 V2 Vi V3 V1 R7 Vo OPAMP + - OUT R4 R3 R8 P.P.5.10 As a voltage follower, ? va = v1 = 2V ? where va is the voltage at the right end of the 20 k? resistor. ? As an inverter, vb = ? Where vb is the voltage at the right end of the 50k? resistor. As a summer ? v0 = ? = [6 - 15] = 9V