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university:courses:electronics:comms-lab-clapp-osc [03 Sep 2014 20:12]
Doug Mercer created
university:courses:electronics:comms-lab-clapp-osc [27 Mar 2019 12:07]
Antoniu Miclaus add ltspice files
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 {{ :​university:​courses:​electronics:​aclap-osc_e2.png?​200 |}} {{ :​university:​courses:​electronics:​aclap-osc_e2.png?​200 |}}
  
-Figure 1 shows a typical Clapp oscillator. The frequency determining series resonant tuned circuit is formed by L<​sub>​1</​sub>​ and C<​sub>​TOT</​sub>​ and is used as the collector load impedance of the common base amplifier Q<​sub>​1</​sub>​. This gives the amplifier a high gain only at the resonant frequency. This configuration of the Hartley oscillator uses a common base amplifier, the base of Q<​sub>​1</​sub>​is biased to an appropriate DC level by resistor divider R<​sub>​1</​sub>​ and R<​sub>​2</​sub>​ but is connected directly to an AC ground by C<​sub>​4</​sub>​. In the common base mode the output voltage waveform at the collector, and the input signal at the emitter are in phase. This ensures that the fraction of the output signal from the node between C<​sub>​1</​sub>​ and C<​sub>​2</​sub>,​ fed back from the tuned collector load to the emitter ​via the coupling capacitor C<​sub>​3</​sub> ​provides the required positive feedback. A large inductance, L<​sub>​2</​sub>,​ provides a DC path for the collector current while presenting a high impedance at the resonate frequency.+Figure 1 shows a typical Clapp oscillator. The frequency determining series resonant tuned circuit is formed by L<​sub>​1</​sub>​ and C<​sub>​TOT</​sub>​ and is used as the collector load impedance of the common base amplifier Q<​sub>​1</​sub>​. A large inductance, L<​sub>​2</​sub>,​ provides a DC path for the collector current while presenting a high impedance at the resonate frequency. This gives the amplifier a high gain only at the resonant frequency. This configuration of the Hartley oscillator uses a common base amplifier, the base of Q<​sub>​1</​sub>​is biased to an appropriate DC level by resistor divider R<​sub>​1</​sub>​ and R<​sub>​2</​sub>​ but is connected directly to an AC ground by C<​sub>​4</​sub>​. In the common base mode the output voltage waveform at the collector, and the input signal at the emitter are in phase. This ensures that the fraction of the output signal from the node between C<​sub>​1</​sub>​ and C<​sub>​2</​sub>,​ fed back from the tuned collector load to the emitter provides the required positive feedback. ​
  
 {{ :​university:​courses:​electronics:​aclap-osc_f1.png?​530 |}} {{ :​university:​courses:​electronics:​aclap-osc_f1.png?​530 |}}
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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\\
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 =====Hardware Setup:===== =====Hardware Setup:=====
  
-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:​clapp_osc-bb.png |}}</​WRAP>​ 
 + 
 +<WRAP centeralign>​ Figure 3 Clapp Oscillator Breadboard circuit </​WRAP>​ 
 + 
 +The green squares indicate where to connect the ADALM2000 ​module AWG, scope channels and power supplies. Be sure to only turn on the power supplies after you double check your wiring.
  
 =====Procedure:​===== =====Procedure:​=====
  
 Having finished construction the Clapp 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 potentiometer for experimentation to find the value that gives the best wave shape and reliable amplitude. Having finished construction the Clapp 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 potentiometer for experimentation to find the value that gives the best wave shape and reliable amplitude.
 +
 +A plot example using R<​sub>​1</​sub>​=10KΩ,​ R<​sub>​2</​sub>​=1KΩ,​ R<​sub>​3</​sub>​=100Ω,​ L<​sub>​1</​sub>​=100uH,​ L<​sub>​2</​sub>​=10uH,​ C<​sub>​1</​sub>​=1nF,​ C<​sub>​2</​sub>​=4.7nF,​ C<​sub>​3</​sub>​=10nF is presented in Figure 4.
 +
 +<WRAP centeralign>​{{ :​university:​courses:​electronics:​clapp_osc-wav.png |}}</​WRAP>​
 +
 +<WRAP centeralign>​ Figure 4 Clapp Oscillator plot </​WRAP>​
  
 =====Questions:​===== =====Questions:​=====
  
-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 voltage at the emitter of Q<​sub>​1</​sub>​. Calculate the average emitter current by measuring the voltage across R<​sub>​3</​sub>​. Compare your measurements with your calculations and simulations. Measure the period (time T) of the output waveform and its frequency (1/T). Compare this measured frequency to what you calculated by F<sub>​R</​sub> = 1 / 2pv(LC).+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 voltage at the emitter of Q<​sub>​1</​sub>​. Calculate the average emitter current by measuring the voltage across R<​sub>​3</​sub>​. Compare your measurements with your calculations and simulations. 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>.
  
 Fill in the table below with the measured frequency for other L<​sub>​1</​sub>​ values for two different values of C<​sub>​3</​sub>​. 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. 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 for two different values of C<​sub>​3</​sub>​. 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. Any of the L<​sub>​1</​sub>​ optional values shown below should give reliable oscillation.
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 |50 uH|  |  | |50 uH|  |  |
 |100 uH|  |  | |100 uH|  |  |
 +
 +<WRAP round download>​
 +**Lab Resources:​**
 +  * Fritzing files: [[ https://​minhaskamal.github.io/​DownGit/#/​home?​url=https://​github.com/​analogdevicesinc/​education_tools/​tree/​master/​m2k/​fritzing/​clapp_osc_bb | clapp_osc_bb]]
 +  * LTspice files: [[ https://​minhaskamal.github.io/​DownGit/#/​home?​url=https://​github.com/​analogdevicesinc/​education_tools/​tree/​master/​m2k/​ltspice/​clapp_osc_ltspice | clapp_osc_ltspice]]
 +</​WRAP>​
  
 **For Further Reading:** **For Further Reading:**
university/courses/electronics/comms-lab-clapp-osc.txt · Last modified: 25 Jun 2020 22:07 (external edit)