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
    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
    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
    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


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

    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.