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0 EE 1270: Introduction to Electric Circuits Lecture 13: Operational Amplifiers Part 2 Chapter 5 The Operational Amplifiers Sections 5.4-5.7 EE 1270 Introduction to Electric Circuits Suketu Naik 1 Operational Amplifiers Pin Diagram Positive Power Supply Negative Power Supply EE 1270 Introduction to Electric Circuits Suketu Naik 2 OpAmp Characteristics vp vo + vn - An Ideal Op amp has infinite open-loop gain, infinite input resistance and zero output resistance When Op amp is connected in the circuit... v p ip vn in vo For an ideal OpAmp vp = vn (voltages at positive input terminal and negative input terminal are equal to each other) ip= in = 0 (currents entering the positive and negative input terminals are zero) EE 1270 Introduction to Electric Circuits Suketu Naik 3 Op-Amp Configurations 1) Inverting Amplifier 2) Non-inverting Amplifier 3) Voltage Follower (or buffer) 4) Summing Amplifier 5) Difference Amplifier EE 1270 Introduction to Electric Circuits Suketu Naik 4 Non-inverting Amplifier Rf vo 1 Rs vg 1) Output and Input signals have same polarity (0 ° phase shift) 2) Non-inverting Amplifier provides positive voltage gain EE 1270 Introduction to Electric Circuits Suketu Naik AP 5.4 5 a) Find the output voltage when Rx=60 kΩ b) How large can Rx be before saturation EE 1270 Introduction to Electric Circuits Suketu Naik 6 Voltage Follower (Buffer) Suppose Rg=Rf=0 (short), Rs=Inifinite (open) Circuit becomes voltage follower, e.g. vo=vi Q: Why use voltage follower (Gain=1)? EE 1270 Introduction to Electric Circuits Suketu Naik 7 Summing Amplifier Rf Rf Rf vo Va Vb Vc Rb Rc Ra A Summing Amplifier combines several inputs and outputs the weighted sum of the inputs EE 1270 Introduction to Electric Circuits Suketu Naik Summing Amplifier: Application 8 Digital to Analog Converter (DAC) Q: Why do we use DAC? EE 1270 Introduction to Electric Circuits Suketu Naik p5.17: Design of a Summing Amp Va Ra Vc Vb Rb Rc 9 Vd Rd Design the Summing Amplifier so that vo 8Va 6Vb 10Vc 6Vd EE 1270 Introduction to Electric Circuits Suketu Naik Difference (Differential) Amplifier 10 Differential Amp rejects Common-mode signal (noise or DC) If Ra/Rb=Rc/Rd (same ratio) then... Rb Vb Va vo Ra A Difference (Differential) Amplifier amplifies the difference between two input signals but rejects signals common to the inputs EE 1270 Introduction to Electric Circuits Suketu Naik Differential Amplifier: Application 11 Instrumentation Amplifer (IA) An Instrumentation Amplifier (IA) is used for precise measurement and amplification with noise reduction in sensors and data acquisition systems EE 1270 Introduction to Electric Circuits Suketu Naik 12 AP5.5a: Differential Amplifier Find range of Va that results in linear operation (avoids saturation) Use Eq (5.22) (because Ra/Rb ≠ Rc/Rd ) Rd ( Ra Rb ) Rb vo vb va Ra ( Rc Rd ) Ra EE 1270 Introduction to Electric Circuits Suketu Naik