EE 40 Fall 2006 Lab 6 Op Amps Op Amps Experiment Guide In this lab we are going to study operational amplifiers and circuits with op amps The op amp chip that we are going to use is LMC 6482 from National Instrument The configuration of the chip is shown below It has two amplifiers in one chip with 8 pins The pin configuration is also shown in the same figure There is a node on the chip indicating pin 1 The power supply to the chip is 4 V for V and 6 V for V in this lab Maximum V V is 30V For more information please refer to the device specification Part 1 Noninverting Amplifier a DC measurements 1 Build up the noninverting amplifier as shown in Fig 1 Use 25V channel and 25V channel of the DC power supply for the VDD and VSS the 25V should be set up to 6V and 25V channel should be set up to 4V Use 6V channel of the DC power supply for Vin and measure both input and output using oscilloscope R1 is 5k and R2 is 5k Change Vin from 2V to 3V to verify the proper amplification range of DC inputs 2 Fix the DC input 0 5V measure the amplifier gain Vout Vin for R2 2 k 5k 10k turn R2 and compare with the calculated gain You need to take out the pot from the circuit to measure its value b AC measurement 1 Now set the input signal to a 1 kHz 0 5 VPP 0 VDC offset on the function generator display Sine wave from the function generator Use a 10k potentiometer as R2 Adjust R2 to see the gain change Can you get a gain less than unity by turning R2 Why 2 Turn the potentiometer R2 until the gain is 2 and then adjust the Vpp and DC offset to the input signal Observe the input and output waveforms as you vary the DC offset for large Vpp say 2 5V Draw the input and output for a case that gives clipping label all the axes and indicate the amplitude and DC offset value Do not take apart your circuit if you want to do the cascaded connection from Part 3 1 EE 40 Fall 2006 Lab 6 Op Amps Part 2 Inverting Amplifier Using the unused op amp of the chip build the inverting amplifier as shown in Fig 2 please use the unused op amp now especially if you want to do part 3 R1 is 5k and R2 is the 10k pot While you are building a circuit it is safer for the circuits if you turn the DC power supply OUTPUT OFF Let the input signal be a 1 kHz 2 5VPP sine wave 0 VDC offset turn R2 to max What s happening to the output signal as you change R2 Adjust the input offset to make the output more complete Now adjust the potentiometer and observe the resulting change in the amplitude and offset of the output Adjust these two parameters until the gain is at its maximum and there s no clipping What range of output voltage do you have in this circuit Verify the correct amplification range of the output signal of both AC and DC signals What is the phase difference between Vout and Vin and where is it from Fig 2 Inverting Amplifier 2 EE 40 Fall 2006 Lab 6 Op Amps Part 3 Cascaded connection optional Now we will study a cascade connection of two amplifiers Connect the output of the non inverting amp to act as the input voltage for the inverting amp Use R2 10k in the inverting circuit and R2 5k in the noninverting circuit The input signal should be a 1 kHz 50mVPP on the function generator display sine wave and you have to pick the correct offset for the circuit to amplify linearly Adjust the input signal to make sure there is no clipping in the circuit Measure the gain of each stage separately and then the overall gain of this cascaded circuit R2 5k R2 10k R1 5k VDD R1 5k VDD VSS Vout VSS Vin Fig 3 Cascade amplifier structure Part 4 Integrator Put a 0 1 uF capacitor instead of R2 in a new inverting amplifier Fig 3 and measure the time constant Use a 60 Hz 500mVPP square wave as input After getting the waveforms and triggering correct measure time constant RC how will you measure it Hint you prelab question 4 Compare measured time constant with theory Now change the function generator back to a sine wave input sweep frequency from 1Hz to 100kHz and observe the change of the gain Fig 4 Integrator 3 EE 40 Fall 2006 Lab 6 Op Amps Part 5 Differentiator Build the inverting amplifier but put 0 1 uF capacitor in stead of R1 as shown in Fig 4 Use R2 5k Input a 500 Hz 500 mVpp triangle wave Zoom into the waveform to measure time constant RC Hint prelab question 5 Compare measured time constant with theory Add DC offset to the input signal is there any change on the output signal Why R2 5k C 0 1uF Vin VDD Vout VSS Fig 5 Differentiator 4
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