[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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