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| university:courses:electronics:electronics-lab-1st [11 Feb 2013 19:23] – [Additional Background on settling time measurements:] Doug Mercer | university:courses:electronics:electronics-lab-1st [03 Nov 2021 20:26] (current) – [Activity:Op Amp Settling Time, For ADALM2000] Doug Mercer |
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| ====== Op Amp Settling Time ====== | ======Activity: Op Amp Settling Time, For ADALM2000====== |
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| ===== Settling Time Background: ===== | ===== Settling Time Background: ===== |
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| ==== Materials: ==== | ==== Materials: ==== |
| Analog Discovery Lab hardware\\ | ADALM2000 Active Learning Module\\ |
| Solder-less breadboard, and jumper wire kit\\ | Solder-less breadboard, and jumper wire kit\\ |
| 2 10 kΩ resistors\\ | 2 10 kΩ resistors\\ |
| 1 10 kΩ potentiometer\\ | 1 10 kΩ potentiometer\\ |
| 2 Schottky diodes (the 1N914 Si diodes supplied in the Analog Parts Kit can be used but will not work as well)\\ | 2 Schottky diodes (the 1N914 Si diodes supplied in the ADALP2000 Analog Parts Kit can be used but will not work as well)\\ |
| 1 OP27 op-amp\\ | 1 OP27 op-amp\\ |
| 1 OP37 op-amp\\ | 1 OP37 op-amp\\ |
| 1 OP97 ( slow settling amplifier not normally supplied with the Analog Parts Kit )\\ | 1 OP97 ( slow settling amplifier )\\ |
| 2 0.1uF Capacitors (used to de-couple the Vp and Vn power supplies)\\ | 2 0.1uF Capacitors (used to de-couple the Vp and Vn power supplies)\\ |
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| ==== Hardware Setup: ==== | ==== Hardware Setup: ==== |
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| Waveform generator 1 should be configured for a 60 KHz square wave with 500 mV amplitude ( 1 volt step ) and 0 volt offset. Scope channel 1 is used to monitor the input square wave and should be set to 500 mV/div and used as the trigger source. Scope channel 2 is used to alternately measure the op amp output, V<sub>2</sub>, and the Error signal at the wiper of the potentiometer. Channel 2 should be set to 500 mV/div when observing the output of the amplifier but should be set to a more sensitive scale of 10 mV/div when observing the Error signal. | Waveform generator 1 should be configured for a 60 KHz square wave 1V amplitude peak-to-peak and 0 volt offset. Scope channel 1 is used to monitor the input square wave and should be set to 500 mV/div and used as the trigger source. Scope channel 2 is used to alternately measure the op amp output, V<sub>2</sub>, and the Error signal at the wiper of the potentiometer. Channel 2 should be set to 500 mV/div when observing the output of the amplifier but should be set to a more sensitive scale of 100 mV/div when observing the Error signal. |
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| | <WRAP centeralign>{{:university:courses:electronics:opamp_settling_time-bb.png|}}</WRAP> |
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| | <WRAP centeralign> Figure 3. Op Amp Settling Time breadboard circuit </WRAP> |
| ==== Procedure: ==== | ==== Procedure: ==== |
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| First use a OP27 amplifier from the Analog Parts Kit for your measurements. The potentiometer should be set near the center of its adjustment range beforehand and should be fine-tuned such that the flat portion of both halves of the signal are nearly equal and centered near 0 Volts, note figure 3. Export the Error waveform showing the settling to both rising and falling input steps for inclusion in your Lab report. You can also store the Error waveform, scope channel 2, for the OP27 as a reference waveform (R1) for future comparison to the settling response of other amplifiers. | First use a OP27 amplifier from the Analog Parts Kit for your measurements. The potentiometer should be set near the center of its adjustment range beforehand and should be fine-tuned such that the flat portion of both halves of the signal are nearly equal and centered near 0 Volts, note figure 4. Export the Error waveform showing the settling to both rising and falling input steps for inclusion in your Lab report. You can also store the Error waveform, scope channel 2, for the OP27 as a reference waveform (R1) for future comparison to the settling response of other amplifiers. |
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| Next replace the OP27 amplifier with a OP37 amplifier from the Parts Kit. Again export the Error waveform showing the settling to both rising and falling input steps for inclusion in your Lab report. Overlay the OP37 settling waveform with the saved reference waveform of the OP27. Compare the settling time and general characteristics of each. You should also again store the Error waveform, scope channel 2, for the OP37 as a reference waveform (R2) for future comparison. | Next replace the OP27 amplifier with a OP37 amplifier from the Parts Kit. Again export the Error waveform showing the settling to both rising and falling input steps for inclusion in your Lab report. Overlay the OP37 settling waveform with the saved reference waveform of the OP27. Compare the settling time and general characteristics of each. You should also again store the Error waveform, scope channel 2, for the OP37 as a reference waveform (R2) for future comparison. |
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| Finally replace the OP37 with the much slower settling OP97 amplifier if you have one available. Again export the Error waveform showing the settling to both rising and falling input steps for inclusion in your Lab report. Overlay the OP97 settling waveform with the saved reference waveforms of the OP27 and OP37. Compare the settling time and general characteristics of each. | Finally replace the OP37 with the much slower settling OP97 amplifier. Again export the Error waveform showing the settling to both rising and falling input steps for inclusion in your Lab report. Overlay the OP97 settling waveform with the saved reference waveforms of the OP27 and OP37. Compare the settling time and general characteristics of each. |
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| {{ :university:courses:electronics:a1st_f3.png?550 |}} | {{ :university:courses:electronics:opamp_settling_time-wav.png |}} |
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| <WRAP centeralign> Figure 3 Example settling waveforms </WRAP> | <WRAP centeralign> Figure 4 Example settling waveforms </WRAP> |
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| ==== Questions: ==== | ==== Questions: ==== |
| ==== Additional Background on settling time measurements: ==== | ==== Additional Background on settling time measurements: ==== |
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| In some cases, a second (very fast) amplifier stage may be used after the false summing node, to increase the Error signal level. Many modern digitizing oscilloscopes, such as the Discovery module, are less sensitive to input overdrive and can be used to measure the Error waveform directly. This must be verified for each oscilloscope by examining the operating manual carefully. Note that a direct measurement allows measurements of settling time in both the inverting and non-inverting modes. An example of the output step response to a flat pulse input for the OP27 and OP97 op amps is shown in figure 3. Notice that the settling time to 1% is approximately 2.8 µSec for the OP27 and 4.2 µSec for the OP97. | In some cases, a second (very fast) amplifier stage may be used after the false summing node, to increase the Error signal level. Many modern digitizing oscilloscopes, such as the ADALM2000 module, are less sensitive to input overdrive and can be used to measure the Error waveform directly. This must be verified for each oscilloscope by examining the operating manual carefully. Note that a direct measurement allows measurements of settling time in both the inverting and non-inverting modes. An example of the output step response to a flat pulse input for the OP27 and OP97 op amps is shown in figure 3. Notice that the settling time to 1% is approximately 2.8 µSec for the OP27 and 4.2 µSec for the OP97. |
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| In making settling time measurements of this type, it is also imperative to use a pulse source capable of generating a pulse of very fast rise and fall times and sufficient flatness. In other words, if the op amp under test has a settling time of 20 nSec to 0.1%, the applied pulse should settle to better than 0.05% in less than 5 nSec. This is beyond the capabilities of the AWG sources built into the Discovery module. | In making settling time measurements of this type, it is also imperative to use a pulse source capable of generating a pulse of very fast rise and fall times and sufficient flatness. In other words, if the op amp under test has a settling time of 20 nSec to 0.1%, the applied pulse should settle to better than 0.05% in less than 5 nSec. This is beyond the capabilities of the AWG sources built into the ADALM2000 module. |
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| This type of source can be expensive, but a simple circuit as shown in Figure 4 can be used with a reasonably flat generator to ensure a flat pulse output. | This type of source can be expensive, but a simple circuit as shown in Figure 5 can be used with a reasonably flat generator to ensure a flat pulse output. |
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| {{ :university:courses:electronics:a1st_f4.png?500 |}} | {{ :university:courses:electronics:a1st_f4.png?500 |}} |
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| <WRAP centeralign> Figure 4: A Simple Flat Pulse Generator </WRAP> | <WRAP centeralign> Figure 5: A Simple Flat Pulse Generator </WRAP> |
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| The circuit in figure 4 works best if low capacitance Schottky diodes are used for D<sub>1</sub>, D<sub>2</sub>, D<sub>3</sub>, and the lead lengths on all the connections are minimized. A short length of 50Ω coax can be used to connect the pulse generator to the circuit, however best results are obtained if the test fixture is connected directly to the output of the generator. The pulse generator is adjusted to output a positive-going pulse at "A" which rises from approximately -1.8 V to +0.5 V in less than 5 nSec (assuming the settling time of the test device is in the order of 20 nSec). Shorter rise times may generate ringing, and longer rise times can degrade the test device settling time; therefore some optimization is required in the actual circuit to get best performance. When the pulse generator output "A" goes above 0 V, D<sub>1</sub> begins to conduct, and D<sub>2</sub>/D<sub>3</sub> are reversed biased. The "0V" region of the signal "B" at the input of the device to be tested is flat "by definition"-neglecting the leakage current and stray capacitance of the D<sub>2</sub>-D<sub>3</sub> series combination. The D<sub>1</sub> diode and its 100O resistor help maintain an approximate 50O termination during the time the pulse at "A" is positive. | The circuit in figure 4 works best if low capacitance Schottky diodes are used for D<sub>1</sub>, D<sub>2</sub>, D<sub>3</sub>, and the lead lengths on all the connections are minimized. A short length of 50Ω coax can be used to connect the pulse generator to the circuit, however best results are obtained if the test fixture is connected directly to the output of the generator. The pulse generator is adjusted to output a positive-going pulse at "A" which rises from approximately -1.8 V to +0.5 V in less than 5 nSec (assuming the settling time of the test device is in the order of 20 nSec). Shorter rise times may generate ringing, and longer rise times can degrade the test device settling time; therefore some optimization is required in the actual circuit to get best performance. When the pulse generator output "A" goes above 0 V, D<sub>1</sub> begins to conduct, and D<sub>2</sub>/D<sub>3</sub> are reversed biased. The "0V" region of the signal "B" at the input of the device to be tested is flat "by definition"-neglecting the leakage current and stray capacitance of the D<sub>2</sub>-D<sub>3</sub> series combination. The D<sub>1</sub> diode and its 100O resistor help maintain an approximate 50O termination during the time the pulse at "A" is positive. |
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| | <WRAP round download> |
| | **Lab Resources:** |
| | * Fritzing files: [[downgit>education_tools/tree/master/m2k/fritzing/opamp_settling_time_bb | opamp_settling_time_bb]] |
| | * LTSpice files: [[downgit>education_tools/tree/master/m2k/ltspice/opamp_settling_time_ltspice | opamp_settling_time_ltspice]] |
| | </WRAP> |
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| ==== For further reading: ==== | ==== For further reading: ==== |
| http://www.analog.com/static/imported-files/tutorials/MT-046.pdf\\ | http://www.analog.com/static/imported-files/tutorials/MT-046.pdf\\ |
| http://www.analog.com/static/imported-files/application_notes/466359863287538299597392756AN359.pdf\\ | http://www.analog.com/static/imported-files/application_notes/466359863287538299597392756AN359.pdf\\ |
| http://en.wikipedia.org/wiki/Settling_time\\ | [[wp>Settling_time|Settling time]] |
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| Return to Lab Activities [[university:courses:electronics:labs|Table of Contents]] | Return to Lab Activities [[university:courses:electronics:labs|Table of Contents]] |
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