Operational Amplifier Circuits - MIT OpenCourseWare
Operational Amplifier Circuits Review: Ideal Op-amp in an open loop configuration RoRi+_VpVnVi+_AViVo+IpIn An ideal op-amp is characterized with infinite open loop gain A The other relevant conditions for an ideal op-amp are: 1. 0IpIn==2. Ri= 3. 0Ro= Ideal op-amp in a negative feedback configuration When an op-amp is arranged with a negative feedback the ideal rules are: 1. : input current constraint 0IpIn==2. : input voltage constraint VnVp= These rules are related to the requirement/assumption for large open-loop gain , and they form the basis for op-amp circuit analysis. A The voltage Vn tracks the voltage Vp and the control of Vn is accomplished via the feedback network. Chaniotakis and Cory.
I3 IF N1 Figure 1. Summing amplifier Current conservation at node N1 gives I12+II+=3IF (1.1) By relating the currents I1, I2 and I3 to their corresponding voltage and resistance by Ohm’s law and noting that the voltage at node N1 is zero (ideal op-amp rule) Equation (1.1) becomes 123 123 VVin in Vin Vout R RRRF ++=− (1.2)
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