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university:courses:electronics:electronics-lab-1 [12 May 2017 14:43] – Antoniu Miclaus | university:courses:electronics:electronics-lab-1 [03 Nov 2021 20:25] (current) – [Activity 1. Simple Op Amps] Doug Mercer | ||
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- | ====== Activity | + | ====== Activity: Simple Op Amps, For ADALM2000====== |
===== Objective: ===== | ===== Objective: ===== | ||
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- | === Simulation: === | ||
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- | Create the voltage follower circuit using ADISim tool as presented in Figure 1.3. | ||
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- | Set the waveform generator in order to output a sine wave with amplitude of 1V (2 Vp-p) and frequency 1kHz. Apply a transient simulation and observe the input and the output waveforms. An example of simulation is presented in Figure 1.4. | ||
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=== Hardware Setup: === | === Hardware Setup: === | ||
- | Using your breadboard and the ADALM2000 power supplies, construct the circuit shown in figure 1.5. Note that the power connections have not been explicitly shown here; it is assumed that those connections must be made in any real circuit (as you did in the previous step), so it is unnecessary to show them in the schematic from this point on. Use jumper wires to connect input and output to the waveform generator and oscilloscope leads. Don’t forget to ground the scope negative input leads C1- and C2- (ground connections are not shown in the schematic). | + | Using your breadboard and the ADALM2000 power supplies, construct the circuit shown in figure 1.3. Note that the power connections have not been explicitly shown here; it is assumed that those connections must be made in any real circuit (as you did in the previous step), so it is unnecessary to show them in the schematic from this point on. Use jumper wires to connect input and output to the waveform generator and oscilloscope leads. Don’t forget to ground the scope negative input leads C1- and C2- (ground connections are not shown in the schematic). |
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- | <WRAP centeralign> | + | <WRAP centeralign> |
=== Procedure: === | === Procedure: === | ||
- | Use the first waveform generator as source Vin to provide a 1V amplitude | + | Use the first waveform generator as source Vin to provide a 2V amplitude |
- | A plot example is presented in Figure 1.6. | + | A plot example is presented in Figure 1.4. |
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==== Slew Rate Limitations: | ==== Slew Rate Limitations: | ||
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- | Set the waveform generator to a square wave signal with a 1V amplitude | + | Set the waveform generator to a square wave signal with a 2V amplitude |
- | A waveform that exemplifies the slew rate is presented in figure 1.8. | + | A waveform that exemplifies the slew rate is presented in figure 1.6. |
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- | <WRAP centeralign> | + | <WRAP centeralign> |
==== Buffering Example: ==== | ==== Buffering Example: ==== | ||
- | The high input resistance of the op amp (zero input current) means there is very little loading on the generator; i.e., no current is drawn from the source circuit and therefore no voltage drops on any internal (Thevenin) resistance. Thus in this configuration the op amp acts like a “buffer” to shield the source from the loading effects from other parts of the system. From the perspective of the load circuit the buffer transforms a non-ideal voltage source into a nearly ideal source. figure 1.9 describes a simple circuit that we can use to demonstrate this feature of a unity-gain buffer. Here the buffer is inserted between a voltage-divider circuit and some “load” resistance: | + | The high input resistance of the op amp (zero input current) means there is very little loading on the generator; i.e., no current is drawn from the source circuit and therefore no voltage drops on any internal (Thevenin) resistance. Thus in this configuration the op amp acts like a “buffer” to shield the source from the loading effects from other parts of the system. From the perspective of the load circuit the buffer transforms a non-ideal voltage source into a nearly ideal source. figure 1.7 describes a simple circuit that we can use to demonstrate this feature of a unity-gain buffer. Here the buffer is inserted between a voltage-divider circuit and some “load” resistance: |
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- | <WRAP centeralign> | + | <WRAP centeralign> |
- | Turn off the power supplies and add the resistors to your circuit as shown in figure 1.9 (note we have not changed the op-amp connections here, we’ve just flipped the op-amp symbol relative to figure 1.2). | + | Turn off the power supplies and add the resistors to your circuit as shown in figure 1.7 (note we have not changed the op-amp connections here, we’ve just flipped the op-amp symbol relative to figure 1.2). |
- | Turn on the power supplies and set the waveform generator to a 1 kHz sine signal with a 2 V amplitude | + | Turn on the power supplies and set the waveform generator to a 1 kHz sine signal with a 4V amplitude |
Remove the 10 kΩ load and substitute a 1 kΩ resistor instead. Record the amplitude. | Remove the 10 kΩ load and substitute a 1 kΩ resistor instead. Record the amplitude. | ||
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=== Background: === | === Background: === | ||
- | Figure 1.10 shows the conventional inverting amplifier configuration with a 10 kΩ “load” resistor at the output. | + | Figure 1.8 shows the conventional inverting amplifier configuration with a 10 kΩ “load” resistor at the output. |
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- | <WRAP centeralign> | + | <WRAP centeralign> |
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- | === Simulation: === | + | |
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- | Create the inverting amplifier circuit using ADISim tool as presented in Figure 1.11. | + | |
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- | <WRAP centeralign> | + | |
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- | Set the waveform generator in order to output a sine wave with amplitude of 1V and frequency 1kHz. Apply a transient simulation and observe the input and the output waveforms. An example of simulation is presented in Figure 1.12. | + | |
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- | {{: | + | |
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=== Hardware Setup: === | === Hardware Setup: === | ||
- | Now assemble the inverting amplifier circuit shown in figure 1.13 using R< | + | Now assemble the inverting amplifier circuit shown in figure 1.9 using R< |
- | Turn on the power supplies and observe the current draw to be sure there are no accidental shorts. Now adjust the waveform generator to produce a 1 volt amplitude, 1 kHz sine wave at the input (Vin), and again display both the input and output on the oscilloscope. Measure and record the voltage gain of this circuit, and compare to the theory that was discussed in class. Export a plot of the input/ | + | Turn on the power supplies and observe the current draw to be sure there are no accidental shorts. Now adjust the waveform generator to produce a 2 volt amplitude |
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- | <WRAP centeralign> | + | <WRAP centeralign> |
This is a good point to comment on circuit debugging. At some point in this class you are likely to have trouble getting your circuit to work. That is not unexpected, nobody is perfect. However, you should not simply assume that a non-working circuit must imply a malfunctioning part or lab instrument. That is almost never true; 99% of all circuit problems are simple wiring or power supply errors. Even experienced engineers will make mistakes from time to time, and consequently, | This is a good point to comment on circuit debugging. At some point in this class you are likely to have trouble getting your circuit to work. That is not unexpected, nobody is perfect. However, you should not simply assume that a non-working circuit must imply a malfunctioning part or lab instrument. That is almost never true; 99% of all circuit problems are simple wiring or power supply errors. Even experienced engineers will make mistakes from time to time, and consequently, | ||
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=== Procedure: === | === Procedure: === | ||
- | Use the first waveform generator as source Vin to provide a 1V amplitude, 1 kHz sine wave excitation to the circuit. Configure the scope so that the input signal is displayed on channel 2 and the output signal is displayed on channel 1. | + | Use the first waveform generator as source Vin to provide a 2V amplitude |
- | A plot example is presented in Figure 1.14. | + | A plot example is presented in Figure 1.10. |
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==== Output Saturation: ==== | ==== Output Saturation: ==== | ||
- | Now change the feedback resistor R< | + | Now change the feedback resistor R< |
==== Summing Amplifier Circuit: ==== | ==== Summing Amplifier Circuit: ==== | ||
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=== Background: === | === Background: === | ||
- | The circuit of figure 1.15 is a basic inverting amplifier with an additional input, called a “summing” amplifier. Using superposition we can show that Vout is a linear sum of Vin1 and Vin2, each with their own unique gain or scale factor. | + | The circuit of figure 1.11 is a basic inverting amplifier with an additional input, called a “summing” amplifier. Using superposition we can show that Vout is a linear sum of Vin1 and Vin2, each with their own unique gain or scale factor. |
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- | <WRAP centeralign> | + | <WRAP centeralign> |
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- | === Simulation: === | + | |
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- | Create the summing amplifier circuit using ADISim tool as presented in Figure 1.16. | + | |
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- | <WRAP centeralign> | + | |
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- | Set the waveform generator in order to output a sine wave with amplitude of 1V and frequency 1kHz for channel 1 and constant 1V for channel 2. Apply a transient simulation and observe the input and the output waveforms. An example of simulation is presented in Figure 1.17. | + | |
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- | {{: | + | |
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=== Hardware Setup: === | === Hardware Setup: === | ||
- | With the power turned off, modify your inverting amplifier circuit as shown in figure 1.18. Use the second waveform generator output for Vin2. Turn the amplitude all the way down to zero so that you can adjust up from zero during the experiment. | + | With the power turned off, modify your inverting amplifier circuit as shown in figure 1.12. Use the second waveform generator output for Vin2. Turn the amplitude all the way down to zero so that you can adjust up from zero during the experiment. |
- | Now apply a 1 volt amplitude sine wave for Vin1 and 1 volts DC for Vin2. Observe and record the input/ | + | Now apply a 2 volt amplitude |
Adjust the DC offset of waveform generator W1 (Vin1) until Vout has zero DC component. Estimate the required DC offset by observing the input waveform on the scope (note: it is not Vin2 , be sure to understand why). | Adjust the DC offset of waveform generator W1 (Vin1) until Vout has zero DC component. Estimate the required DC offset by observing the input waveform on the scope (note: it is not Vin2 , be sure to understand why). | ||
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=== Procedure: === | === Procedure: === | ||
- | Use the first waveform generator as source Vin to provide a 1V amplitude, 1 kHz sine wave excitation to the circuit. The second waveform generator is used to generate 1V constant voltage. Configure the scope so that the input signal is displayed on channel 2 and the output signal is displayed on channel 1. | + | Use the first waveform generator as source Vin to provide a 2V amplitude |
- | A plot example is presented in Figure 1.19. | + | A plot example is presented in Figure 1.13. |
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- | <WRAP centeralign> | + | <WRAP centeralign> |
==== Non-Inverting Amplifier: ==== | ==== Non-Inverting Amplifier: ==== | ||
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=== Background: === | === Background: === | ||
- | The non-inverting amplifier configuration is shown in figure 1.20. Like the unity-gain buffer, this circuit has the (usually) desirable property of high input resistance, so it is useful for buffering non-ideal sources: | + | The non-inverting amplifier configuration is shown in figure 1.14. Like the unity-gain buffer, this circuit has the (usually) desirable property of high input resistance, so it is useful for buffering non-ideal sources: |
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- | <WRAP centeralign> | + | <WRAP centeralign> |
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- | === Simulation: === | + | |
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- | Create the non-inverting amplifier circuit using ADISim tool as presented in Figure 1.21. | + | |
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- | <WRAP centeralign> | + | |
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- | Set the waveform generator in order to output a sine wave with amplitude of 1V and frequency 1kHz for channel 1. Apply a transient simulation and observe the input and the output waveforms. An example of simulation is presented in Figure 1.22. | + | |
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- | {{: | + | |
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=== Hardware Setup: === | === Hardware Setup: === | ||
- | Assemble the non-inverting amplifier circuit shown in figure 1.23. Remember to shut off the power supplies before assembling the new circuit. Start with R< | + | Assemble the non-inverting amplifier circuit shown in figure 1.15. Remember to shut off the power supplies before assembling the new circuit. Start with R< |
- | Apply a 1 volt amplitude, 1 kHz sine wave at the input, and display both input and output on the scope. Measure the voltage gain of this circuit, and compare to the theory discussed in class. Export a plot of the waveforms and include it in your lab report. | + | Apply a 2 volt amplitude |
Increase the feedback resistor (R< | Increase the feedback resistor (R< | ||
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- | <WRAP centeralign> | + | <WRAP centeralign> |
=== Procedure: === | === Procedure: === | ||
- | Use the first waveform generator as source Vin to provide a 1V amplitude, 1 kHz sine wave excitation to the circuit. Configure the scope so that the input signal is displayed on channel 2 and the output signal is displayed on channel 1. | + | Use the first waveform generator as source Vin to provide a 2V amplitude |
- | A plot example is presented in Figure 1.24. | + | A plot example is presented in Figure 1.16. |
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- | <WRAP centeralign> | + | <WRAP centeralign> |
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- | ===== 1.3 Using an Op-Amp as a Comparator ===== | + | |
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- | === Background: === | + | |
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- | The high intrinsic gain of the op-amp and the output saturation effects can be exploited by configuring the op-amp as a comparator as in figure 1.25. This is essentially a binary-state decision-making circuit: if the voltage at the “+” terminal is greater than the voltage at the “-” terminal, Vin > Vref , the output goes “high” (saturates at its maximum value). Conversely if Vin < Vref the output goes “low”. The circuit compares the voltages at the two inputs and generates an output based on the relative values. Unlike all the previous circuits there is no feedback between the input and output; we say that the circuit is operating “open-loop”. | + | |
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- | {{ : | + | |
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- | === Simulation: === | + | |
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- | Create the op-amp comparator circuit using ADISim tool as presented in Figure 1.26. | + | |
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- | <WRAP centeralign> | + | |
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- | Set the waveform generator in order to output a sine wave with amplitude of 1V and frequency 1kHz for channel 1 and 0V constant voltage for channel 2. Apply a transient simulation and observe the input and the output waveforms. An example of simulation is presented in Figure 1.27. | + | |
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- | {{: | + | |
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- | === Hardware Setup: === | + | |
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- | Comparators are used in different ways, and in future sections we will see them in action in several labs. Here we will use the comparator in a common configuration that generates a square wave with a variable pulse width: | + | |
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- | Start by shutting off the power supplies and assemble the circuit. As with the summing amplifier circuit earlier, use the second waveform generator output for the DC source Vref , and turn the amplitude to zero and the output offset all the way down so that you can adjust up from zero during the experiment. | + | |
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- | Again configure the waveform generator Vin for a 2V amplitude sine wave at 1 kHz. With the power supply on and Vref at zero volts, export the output waveform. | + | |
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- | Now slowly increase Vref and observe what happens. Record the output waveform for Vref = 1V. Keep increasing Vref until it exceeds 2V and observe what happens. Can you explain this? | + | |
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- | Repeat the above for a triangular input waveform and record your observations for your lab report. | + | |
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- | {{: | + | |
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- | === Procedure: === | + | |
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- | Use the first waveform generator as source Vin to provide a 1V amplitude, 1 kHz sine wave excitation to the circuit. Configure the scope so that the input signal is displayed on channel 2 and the output signal is displayed on channel 1. | + | |
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- | A plot example is presented in Figure 1.24. | + | |
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- | {{: | + | |
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- | <WRAP centeralign> | + | |
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- | ==== Extra Credit ==== | + | |
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- | For experimenters who finish early or want an additional challenge, see if you can modify the comparator circuit using your red and green LEDs (from the last lab) at the output so that the red LED lights for negative voltages and the green LED lights for positive voltages. Turn down the frequency to 1Hz (or less) so you can see them turn on-and-off in real time. Don’t forget that the LEDs will need a current-limiting resistor so that the current through it is no more than 20mA. | + | |
=== Congratulations! You have now completed Lab Activity 1 === | === Congratulations! You have now completed Lab Activity 1 === | ||
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■ Slew rate: discuss how you measured and computed the slew rate in the unity-gain buffer configuration, | ■ Slew rate: discuss how you measured and computed the slew rate in the unity-gain buffer configuration, | ||
- | ■ Buffering: explain why the buffer amplifier in figure 1.6 allowed the voltage divider circuit to function perfectly with differently load resistances. | + | ■ Buffering: explain why the buffer amplifier in figure 1.7 allowed the voltage divider circuit to function perfectly with differently load resistances. |
■ Output saturation: explain your observations of output voltage saturation in the inverting amplifier configuration and your estimate of the internal voltages drops. How close does the output come to the supply rails in this experiment and also later when used as a comparator with different power-supply voltages? Can you guess what the output voltage swing would be for an op-amp that is advertised as a “rail-to-rail” device? | ■ Output saturation: explain your observations of output voltage saturation in the inverting amplifier configuration and your estimate of the internal voltages drops. How close does the output come to the supply rails in this experiment and also later when used as a comparator with different power-supply voltages? Can you guess what the output voltage swing would be for an op-amp that is advertised as a “rail-to-rail” device? | ||
- | ■ Summing circuit: using superposition, | + | ■ Summing circuit: using superposition, |
■ Comparator: discuss your measurements and what would happen if the polarity of Vref is reversed | ■ Comparator: discuss your measurements and what would happen if the polarity of Vref is reversed | ||
+ | \\ | ||
+ | \\ | ||
+ | <WRAP round download> | ||
+ | **Resources: | ||
+ | * Fritzing files: [[downgit> | ||
+ | * LTSpice files: [[downgit> | ||
+ | </ | ||
+ | |||
+ | **Continue to next Op Amp Lab Activity: [[university: | ||
- | **Return to Lab Activity [[university: | + | **More on Op Amps in amplifier configuration: |
+ | \\ | ||
+ | \\ | ||
+ | **Return to Lab Activity: [[university: | ||