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| university:courses:electronics:electronics-lab-4 [27 Oct 2012 18:10] – created Doug Mercer | university:courses:electronics:electronics-lab-4 [23 Mar 2017 15:53] – [Directions and Setup:] Doug Mercer |
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| ===== Materials: ===== | ===== Materials: ===== |
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| Analog Discovery Lab Instrument Hardware\\ | ADALM2000 Active Learning Module\\ |
| Solder-less Breadboard\\ | Solder-less Breadboard\\ |
| 1 - 100KΩResistors\\ | 1 - 100KΩResistors\\ |
| ===== Directions and Setup: ===== | ===== Directions and Setup: ===== |
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| Build the simple curve tracer circuit shown in figure 1. The green boxes indicate where to connect the Discovery Board. Using the custom waveform editor in the Waveforms AWG tool, construct a stair-step waveform with 5 levels. Be sure to reset so that you are starting with flat line at 0%. First set the type to constant. Then with start set to 0%, length set to 20% and offset set to -100% click on generate function. There should now be a line at -100% from 0 to 20%. Next change the start to 20% and the offset to -50% and then click on generate function again. There should now be a line at -50% from 20% to 40%. Next set the offset to +50% and the start to 60% and then click on generate function again. There should now be a line at 0% from 40% to 60% and a line at 50% from 60% to 80%. Finally set the offset to 100% and start to 80% and click on generate function one last time. There should now be a final line at 100% from 80% to 100%. Click on save and your new waveform should be in channel 2. Now at this point set the frequency to 40Hz, the amplitude to 2 V and the offset to 2.6 V. The waveform in the display should start at 0.6V and increase in 1 V increments to 4.6 V (0.6, 1.6, 2.6, 3.6, 4.6) Each step should be 5 mSec long for a total of 25 mSec. In AWG channel 1 configure a triangle wave with an amplitude of 2.5 V and an offset of 2.5V (wave should swing from 0 to 5V). Set the frequency to 200 Hz ( 5 times the 40 Hz of channel 2). Comparing the waveforms in channel 1 and channel 2, the triangle wave in channel 1 should go through one cycle from 0 to 5 V and back to zero during the time of one step in the waveform in channel 2. It will probably be necessary to set the phase of channel 1 to 270 degrees to make them line up in this way. | Build the simple curve tracer circuit shown in figure 1. The green boxes indicate where to connect the ADALM2000. Using the custom waveform editor in the Scopy AWG tool, construct a stair-step waveform with 5 levels. Be sure to reset so that you are starting with flat line at 0%. First set the type to constant. Then with start set to 0%, length set to 20% and offset set to -100% click on generate function. There should now be a line at -100% from 0 to 20%. Next change the start to 20% and the offset to -50% and then click on generate function again. There should now be a line at -50% from 20% to 40%. Next set the offset to +50% and the start to 60% and then click on generate function again. There should now be a line at 0% from 40% to 60% and a line at 50% from 60% to 80%. Finally set the offset to 100% and start to 80% and click on generate function one last time. There should now be a final line at 100% from 80% to 100%. Click on save and your new waveform should be in channel 2. Now at this point set the frequency to 40Hz, the amplitude to 2 V and the offset to 2.6 V. The waveform in the display should start at 0.6V and increase in 1 V increments to 4.6 V (0.6, 1.6, 2.6, 3.6, 4.6) Each step should be 5 mSec long for a total of 25 mSec. In AWG channel 1 configure a triangle wave with an amplitude of 2.5 V and an offset of 2.5V (wave should swing from 0 to 5V). Set the frequency to 200 Hz ( 5 times the 40 Hz of channel 2). Comparing the waveforms in channel 1 and channel 2, the triangle wave in channel 1 should go through one cycle from 0 to 5 V and back to zero during the time of one step in the waveform in channel 2. It will probably be necessary to set the phase of channel 1 to 270 degrees to make them line up in this way. |
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| You should export your newly created stair-step waveform to a .csv file for future use. | You should export your newly created stair-step waveform to a .csv file for future use. |
| ===== Materials: ===== | ===== Materials: ===== |
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| Analog Discovery Lab Instrument Hardware\\ | ADALM2000 Active Learning Module\\ |
| Solder-less Breadboard\\ | Solder-less Breadboard\\ |
| 1 - Dual Op AMP (such as ADTL082)\\ | 1 - Dual Op AMP (such as ADTL082)\\ |
| ===== Directions and Setup: ===== | ===== Directions and Setup: ===== |
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| Below are schematics for both a common emitter and a common base BJT curve tracer test circuit for use with the Discovery Lab hardware. It uses one dual opamp (ADTL082) powered from the +/- 5 Volt board supplies. In the common emitter configuration, one opamp serves as a virtual ground at the base terminal to convert the voltage steps from waveform generator W2 into base current steps through a 10KΩ resistor. The collector voltage is swept using a ramp from generator W1. V<sub>CE</sub> is measured differentially by scope inputs 1+, 1-. The collector current, I<sub>C</sub> is measured by scope inputs 2+, 2- differentially across a 100Ω resistor. A ratio of 100 for the base and collector resistors is used because beta, the collector current to base current gain, is often approximately 100. The voltage on the base terminal can be offset to either +2.5V or -2.5V (or 0V) to increase the possible V<sub>CE</sub> swing (by -2.5 for NPN or +2.5 for PNP). The +2.5V is generated by a voltage divider from the +5V supply and the -2.5V is generated by inverting the +2.5V with the second opamp in the dual op-amp (ADTL082). The base and emitter connection can be interchanged to configure the device under test (DUT) in the common base mode. The resistor values are changed to 1KΩ for both in this configuration. This ratio of one is appropriate given that alpha, the ratio of emitter current to collector current, is very close to one. The voltage from W2 now sets the emitter current and the ramp on W1 sweeps the V<sub>CB</sub> and is measured differentially with 1+, 1-. The collector current I<sub>C</sub> is measured differentially across the 1KΩ resistor with 2+, 2-. | Below are schematics for both a common emitter and a common base BJT curve tracer test circuit for use with the ADALM2000. It uses one dual opamp (ADTL082) powered from the +/- 5 Volt board supplies. In the common emitter configuration, one opamp serves as a virtual ground at the base terminal to convert the voltage steps from waveform generator W2 into base current steps through a 10KΩ resistor. The collector voltage is swept using a ramp from generator W1. V<sub>CE</sub> is measured differentially by scope inputs 1+, 1-. The collector current, I<sub>C</sub> is measured by scope inputs 2+, 2- differentially across a 100Ω resistor. A ratio of 100 for the base and collector resistors is used because beta, the collector current to base current gain, is often approximately 100. The voltage on the base terminal can be offset to either +2.5V or -2.5V (or 0V) to increase the possible V<sub>CE</sub> swing (by -2.5 for NPN or +2.5 for PNP). The +2.5V is generated by a voltage divider from the +5V supply and the -2.5V is generated by inverting the +2.5V with the second opamp in the dual op-amp (ADTL082). The base and emitter connection can be interchanged to configure the device under test (DUT) in the common base mode. The resistor values are changed to 1KΩ for both in this configuration. This ratio of one is appropriate given that alpha, the ratio of emitter current to collector current, is very close to one. The voltage from W2 now sets the emitter current and the ramp on W1 sweeps the V<sub>CB</sub> and is measured differentially with 1+, 1-. The collector current I<sub>C</sub> is measured differentially across the 1KΩ resistor with 2+, 2-. |
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| {{ :university:courses:electronics:a4_f4.png?500 |}} | {{ :university:courses:electronics:a4_f4.png?500 |}} |
| This same circuit can be used to measure PNP devices by simply configuring the ramp signal to be positive, i.e. from 0V to the maximum positive swing of the source. | This same circuit can be used to measure PNP devices by simply configuring the ramp signal to be positive, i.e. from 0V to the maximum positive swing of the source. |
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| For further reading on the Howland current source: | ==== For further reading on the Howland current source: ==== |
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| [[http://www.cirrus.com/en/pubs/whitePaper/199210-Apex-Versatile_current_source_circuits.pdf|http://www.cirrus.com/en/pubs/whitePaper/199210-Apex-Versatile_current_source_circuits.pdf]] | [[http://www.cirrus.com/en/pubs/whitePaper/199210-Apex-Versatile_current_source_circuits.pdf|http://www.cirrus.com/en/pubs/whitePaper/199210-Apex-Versatile_current_source_circuits.pdf]] |
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| [[http://falstad.com/circuit/e-howland.html|http://falstad.com/circuit/e-howland.html]] | [[http://falstad.com/circuit/e-howland.html|http://falstad.com/circuit/e-howland.html]] |
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| | **Return to Lab Activity [[university:courses:electronics:labs|Table of Contents]]** |
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