[time-nuts] Help with TCXO

Attila Kinali attila at kinali.ch
Mon Nov 28 02:36:48 EST 2011

On Mon, 28 Nov 2011 16:15:37 +1100
Michael Malloy <mechano at gmail.com> wrote:

> Hi all I ordered a 8.192MHZ TCXO 1.0PPM
> Now it was supposed to have a clipped sine wave output? however it
> looks more like a saw tooth, I assumed a clipped sine would be a sine
> wave with the peaks clipped, I am running this through
> a 150pF cap and then using a inverter amplifier i.e. 74HC04 with a 1M
> resistor from input to output.
> am I over loading or loading down the the oscillator, or should I be
> changing the buffer capacitor?
> I mean the circuit is working but its not 45/55 duty cycle
> the out put looks like the first 0 -90 degrees of a sine wave then
> drops to zero stays there for about 20% of the duty cycle then ramps
> back up?

Do you measure the TCXO raw, w/o any circuitry attached?
Because this sounds rather like that the 74ZHC04 is messing
with the signal. Maybe the 1M resistor isnt really 1M?

Other than that, i would feed the output directly to
a 74HC14 (schmitt trigger input) to square it. If you
want to have precise or adjustable duty cycle, you can also
use a comparator (but make sure to include enough hysteresis,
otherwise the comparator might oscillate)

			Attila Kinali

Why does it take years to find the answers to
the questions one should have asked long ago?

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