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university:courses:electronics:comms-lab-colpitts-osc [03 Sep 2014 20:26]
dmercer [Questions:]
university:courses:electronics:comms-lab-colpitts-osc [05 Mar 2019 12:57]
amiclaus [Questions:]
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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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 =====Directions:​===== =====Directions:​=====
  
-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>​. ​
  
 {{ :​university:​courses:​electronics:​acol-osc_f2.png?​530 |}} {{ :​university:​courses:​electronics:​acol-osc_f2.png?​530 |}}
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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:​colpitts_osc-bb.png|}}</​WRAP>​ 
 + 
 +<WRAP centeralign>​ Figure 3 Colpitts Oscillator breadboard circuit</​WRAP>​ 
 + 
 +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.
  
 =====Procedure:​===== =====Procedure:​=====
  
 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.
 +
 +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.
 +
 +<WRAP centeralign>​{{ :​university:​courses:​electronics:​colpitts_osc-wav.png|}}</​WRAP>​
 +
 +<WRAP centeralign>​ Figure 4 Colpitts Oscillator breadboard plot</​WRAP>​
  
 =====Questions:​===== =====Questions:​=====
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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/​colpitts_osc_bb | colpitts_osc_bb]]
 +</​WRAP>​
  
 **For Further Reading:** **For Further Reading:**
university/courses/electronics/comms-lab-colpitts-osc.txt · Last modified: 27 Mar 2019 12:07 by amiclaus