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Project Notes

#687 Crystal-locked 455kHz Oscillator

Testing a 455kHz crystal-locked Pierce oscillator using CD4001 CMOS NOR gates.



This circuit is a variation on the theme from LEAP#656 Crystal-Locked Schmitt Oscillator using NOR gates and a 4MHz crystal.

Circuit Design

Key design notes:

  • Instead of simple inverters, the design uses NOR gates from a CD4001 chip. The NOR gate may either be wired:
    • both inputs tied together, so the output is always the inverse of the input
    • one input tied to ground, so the output is always the inverse of the other input
  • With a 455kHHz crystal, relatively large stabilization capacitors are required to maintain oscilation (in this case >=300pF). The mis-matched stabilization capacitors help ensure oscillation starts.
  • A feedback resistor is not essential and has been left out as the frequency is relatively low.




Test Results

Measuring 452.3kHz, with scope connections as follows:

  • CH1 Yellow: buffered oscillator output
  • CH2 Blue: oscillator output

At this frequency, the buffered output is a nice square wave.


Credits and References

About LEAP#687 CMOS/TTLOscillators
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