I created a PCB which needs to have a solid and precious clock source. For this purpose I used a Dual Inverter with Schmitt trigger (NC7WZ14).


Now CLKI seems to generate 66kHz square signals (measured by an oscilloscope at the point of CLKI).

Scope image

Why is this circuit not generating 11.0592MHz for me?


Referenced from: https://www.electronics-tutorials.ws/oscillator/crystal.html, at section "CMOS Crystal Oscillator".


  • \$\begingroup\$ Why R8? Feels like you're mixing Opamp and Schmitt-Trigger circuits \$\endgroup\$ – Marcus Müller Mar 18 '18 at 13:36
  • \$\begingroup\$ I found it online. What do you recommend for me to change? \$\endgroup\$ – Daniel Mar 18 '18 at 13:39

The problem is that you are using a Schmitt trigger for your inverter. An oscillator like the one you show in your schematic depends on the inverter acting like a linear amplifier due to the feedback, and this is not possible for a Schmitt trigger inverter.


Take a look at this reference which explains using CMOS gates in oscillators.

| improve this answer | |
  • \$\begingroup\$ You suggest me to change the inverter to a non-schmitt trigger one? \$\endgroup\$ – Daniel Mar 18 '18 at 13:40
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    \$\begingroup\$ Yes. Take a look at the reference I added to the answer. \$\endgroup\$ – crj11 Mar 18 '18 at 13:45
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    \$\begingroup\$ +1 Not only non-ST but it should be an unbuffered type. \$\endgroup\$ – Spehro Pefhany Mar 18 '18 at 14:56
  • \$\begingroup\$ Thank you. Will make an update once I got the new part and tried out. \$\endgroup\$ – Daniel Mar 18 '18 at 16:00
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    \$\begingroup\$ I have successfully made an oscillator using standard buffered inverters, but I took advantage of a 'feature' that they had issues with ground bounce. (Part was 74LCX04). \$\endgroup\$ – Peter Smith Mar 18 '18 at 16:20

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