Best way to Create A Colpitts Circuit

Discussion in 'Digital Circuit Design' started by Parkourguy, May 8, 2019.

  1. Parkourguy

    Thread Starter New Member

    Apr 9, 2019
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    Hello, I'm new to circuit design with general beginner knowledge into circuitry, signaling and systems. I would like to try on a project on constructing a RF circuit to generate an output of 10MHz square wave frequency with a 5 volt output. Ive done a bit of research and would think that a Colpitts Circuit with a NPN transistor would be the best way to achieve this. I would like to know other peoples opinion on this and what points I should cover on this. Thank You
     
  2. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    For a 10MHz square wave, a logic gate oscillator is probably the way to go. Scroll down here to 'CMOS Crystal Oscillator'.
     
  3. Parkourguy

    Thread Starter New Member

    Apr 9, 2019
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    I found the design you posted which was a great much help. A few questions if you could answer for me would also be great. I heard that a schmitt inverter as the first inverter would cause frequency distortion, so a 74HC04 inverter would be the best option as the first and second inverter rather than a Schmitt inverter. Would that be the best way to creating this crystal oscillator?
     
  4. DickCappels

    Moderator

    Aug 21, 2008
    5,577
    1,745
    If you use a Schmitt trigger you can do it with three components (plus power supply bypass capacitor, not shown.)

    upload_2019-5-15_14-42-52.png
    I had a 74HC14 running at 15 MHz in this circuit. Higher frequencies are possible.

    Colpitts oscillators make sine waves, or very nearly so, if you started with a Colpitts oscillator you would need one or more additional stages to make a square wave out of it. The spectrum of a square wave is the sum of several odd harmonics -the more harmonics the more square the waveform. Figure you would probably want a bandwidth of at least 50 MHz for a 10 Mhz square wave.
     
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