MASSACHUSETTS INSTITUTE OF TECHNOLOGY 6 071 Introduction to Electronics Signals and Measurement Spring 2006 Laboratory 20 Introduction to the Op Amp In this lab we will explore the fundamental non inverting op amp amplifier circuit To construct the circuit we will use the LF356 op amp The 356 is a good cheap easy to work with op amp well suited to most basic circuits More expensive op amps tend to sacrifice op amp ideality finite input current stability power supply reject etc for specific purposes high speed low noise etc and can be much more difficult to work with The data sheet for the 356 is available in the class web site The pinout of the 356 is the same as that of another widely used op amp the 741 and is shown below Use this op amp to construct the circuit shown below Select R1 and R2 to achieve a gain of 3 R2 I2 15V R1 Vn Vi I1 Ro Ri Vo AVi RL 15V IL Vin Make the following connections to your data acquisition system 22 071 6 071 Spring 2006 Chaniotakis Cory Page1 ACH0 Supply Vin ACH1 Vo ACH2 Vn 15 Volts VDD 15 Volts VSS ACH0 ACH1 ACH2 Ground Down load the LabView instrument called Op Amp1 vi from the Labs section Run the instrument and answer the following questions 1 For Vin 2 Volt measure and record the following Vn Vo I1 I2 IL Compare I1 and I2 How close are they What about Vn and Vi 2 Does I1 I2 IL satisfy KCL If not what other currents should be considered 22 071 6 071 Spring 2006 Chaniotakis Cory Page2 3 A is the open loop gain of the op amp Ri and Ro are the input and output resistance of the op amp device NOT THE CIRCUIT THAT YOU HAVE CONSTRUCTED What value of A results in a 5 difference between the measured and the simulated output voltage Vo 4 For Vin 5Volts what is the output 5 For Vin 2 Volts What is Vo 6 Arrange your circuit to be a follower by making R2 0 and R1 infinity Observe the circuit operation Justify your observation 22 071 6 071 Spring 2006 Chaniotakis Cory Page3
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