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| university:courses:electronics:comms-lab-colpitts-osc [03 Sep 2014 20:19] – created Doug Mercer | university:courses:electronics:comms-lab-colpitts-osc [05 Mar 2019 12:57] – [Questions:] Antoniu Miclaus |
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| =====Materials:===== | =====Materials:===== |
| | ADALM2000 Active Learning Module\\ |
| Analog Discovery Lab hardware\\ | |
| Solder-less breadboard, and jumper wire kit\\ | Solder-less breadboard, and jumper wire kit\\ |
| 1 - 2N3904 NPN transistor\\ | 1 - 2N3904 NPN transistor\\ |
| =====Directions:===== | =====Directions:===== |
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| Build the Colpitts Oscillator shown in figure 2 using your solder-less breadboard. Pick standard values from your parts kit for bias resistors R<sub>1</sub> and R<sub>2</sub> such that with emitter resistor R<sub>3</sub>set to 1 KΩ, the collector current in NPN transistor Q<sub>1</sub> is approximately 1 mA. The frequency of the oscillator can be from around 500 KHz to 2 MHz depending on the values chosen for C<sub>1</sub>, C<sub>2</sub> and L<sub>1</sub>. Start with L<sub>1</sub> = 100 nH and C<sub>1</sub> = 4.7 nF and C<sub>2</sub> = 1 nF. This oscillator circuit can produce a sine wave output in excess of 10 Vpp at an approximate frequency set by the value chosen for L<sub>1</sub>. | Build the Colpitts Oscillator shown in figure 2 using your solder-less breadboard. Pick standard values from your parts kit for bias resistors R<sub>1</sub> and R<sub>2</sub> such that with emitter resistor R<sub>3</sub>set to 1 KΩ, the collector current in NPN transistor Q<sub>1</sub> is approximately 1 mA. The frequency of the oscillator can be from around 500 KHz to 2 MHz depending on the values chosen for C<sub>1</sub>, C<sub>2</sub> and L<sub>1</sub>. Start with L<sub>1</sub> = 100 uH and C<sub>1</sub> = 4.7 nF and C<sub>2</sub> = 1 nF. This oscillator circuit can produce a sine wave output in excess of 10 Vpp at an approximate frequency set by the value chosen for L<sub>1</sub>. |
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| {{ :university:courses:electronics:acol-osc_f2.png?530 |}} | {{ :university:courses:electronics:acol-osc_f2.png?530 |}} |
| =====Hardware Setup:===== | =====Hardware Setup:===== |
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| The green squares indicate where to connect the Discovery module AWG, scope channels and power supplies. Be sure to only turn on the power supplies after you double check your wiring. | <WRAP centeralign>{{ :university:courses:electronics:colpitts_osc-bb.png|}}</WRAP> |
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| | <WRAP centeralign> Figure 3 Colpitts Oscillator breadboard circuit</WRAP> |
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| | The green squares indicate where to connect the ADALM2000module AWG, scope channels and power supplies. Be sure to only turn on the power supplies after you double check your wiring. |
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| =====Procedure:===== | =====Procedure:===== |
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| Having finished construction the Colpitts oscillator check that the circuit is oscillating correctly by turning on both the + and - 5 V power supplies and connecting one of the oscilloscope channels to the output terminal. It may be found that the value of R<sub>3</sub> is fairly critical, producing either a large distorted waveform or an intermittent low or no output. To find the best value for R<sub>3</sub>, it could be replaced by a 1 KΩ or 5 KΩ potentiometer for experimentation to find the value that gives the best wave shape and reliable amplitude. The optimal value for R<sub>3</sub> may change depending on the resonate frequency. | Having finished construction the Colpitts oscillator check that the circuit is oscillating correctly by turning on both the + and - 5 V power supplies and connecting one of the oscilloscope channels to the output terminal. It may be found that the value of R<sub>3</sub> is fairly critical, producing either a large distorted waveform or an intermittent low or no output. To find the best value for R<sub>3</sub>, it could be replaced by a 1 KΩ or 5 KΩ potentiometer for experimentation to find the value that gives the best wave shape and reliable amplitude. The optimal value for R<sub>3</sub> may change depending on the resonate frequency. |
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| | A plot example using R<sub>1</sub>=10KΩ, R<sub>2</sub>=1KΩ, C<sub>1</sub>=4.7nF, C<sub>2</sub>=1nF is presented in Figure 4. |
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| | <WRAP centeralign>{{ :university:courses:electronics:colpitts_osc-wav.png|}}</WRAP> |
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| | <WRAP centeralign> Figure 4 Colpitts Oscillator breadboard plot</WRAP> |
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| =====Questions:===== | =====Questions:===== |
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| Measure the peak to peak output voltage of the output. Measure the DC ( average ) level of the output waveform at the collector of Q<sub>1</sub> and on the other (output) side of AC coupling capacitor C<sub>4</sub>. Measure the period (time T) of the output waveform and its frequency (1/T). Compare this measured frequency to what you calculated by | Measure the peak to peak output voltage of the output. Measure the DC ( average ) level of the output waveform at the collector of Q<sub>1</sub> and on the other (output) side of AC coupling capacitor C<sub>4</sub>. Measure the period (time T) of the output waveform and its frequency (1/T). Compare this measured frequency to what you calculated by:\\ |
| <m> F_R = 1 / {2 pi sqrt(LC)}</m>. | <m>F_R = 1 / {2 pi sqrt(LC)}</m>. |
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| Fill in the table below with the measured frequency for other L<sub>1</sub> values. Use the values in the table as suggested options but try to include as many different values as possible using series and parallel combinations of the inductors supplied in your parts kit. For example a 20 uH inductor value can be made from two 10 uH inductors in series and likewise a 50 uH value can be obtained by connecting two 100 uH inductors in parallel. Any of the L<sub>1</sub> optional values shown below should give reliable oscillation. | Fill in the table below with the measured frequency for other L<sub>1</sub> values. Use the values in the table as suggested options but try to include as many different values as possible using series and parallel combinations of the inductors supplied in your parts kit. For example a 20 uH inductor value can be made from two 10 uH inductors in series and likewise a 50 uH value can be obtained by connecting two 100 uH inductors in parallel. Any of the L<sub>1</sub> optional values shown below should give reliable oscillation. |
| |50 uH| | | | |50 uH| | | |
| |100 uH| | | | |100 uH| | | |
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| | <WRAP round download> |
| | **Lab Resources:** |
| | * Fritzing files: [[ https://minhaskamal.github.io/DownGit/#/home?url=https://github.com/analogdevicesinc/education_tools/tree/master/m2k/fritzing/colpitts_osc_bb | colpitts_osc_bb]] |
| | </WRAP> |
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| **For Further Reading:** | **For Further Reading:** |
