I am using a K65 tower eval board where I have a clipped sine-wave oscillator that has about 1 volt peak to peak. I feed that into a 1000 capacitor and then an invertor whose output feeds back through a 1 meg resistor to the input.
The resulting output is a 3 volt peak to peak square-wave as would be expected. As soon as it is feed into the ext osc in pin, the square-wave is distorted (almost positively saturated).
Do I have something configured incorrectly?
Hi Calvin,
After have a brief look through your question, I'm still not very clear with it.
Do you mean to use a external clipped sine-wave oscilator to feed the MCU instead of the FL1600084 on the board?
Have a great day,
Ping
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Yes. We are using 32.768 MHz oscillator clock instead of the crystal.
Hi Calvin,
Please refer to the circuit design and the RF can select the 10M.
Have a great day,
Ping
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The MCU controls a 16-bit DAC to a VCTCXO which feeds a 1000pF capacitor to an invertor back to the EXTAL pin.
I have seen this which is supposed to reduce the load on the VCTCXO but I haven't attempted it yet.
Hi Calvin,
How about let the oscillator output connect the MCU directly?
Have a great day,
Ping
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The output is only 1 volt peak to peak and not enough to clock.
Maybe there is a setting that can apply gain on the input without using the output pin.
Hi Calvin,
Thanks for your reply.
For me, I'd highly recommend to choose another oscillator instead of the old one.
I think gain the the square-wave by using the external circuit to feed the MCU, maybe it can make it. however it actually make the whole circuit more complicated and unstable.
Have a great day!
Ping