#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.
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.
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.