[time-nuts] Triangle Waves

Joseph M Gwinn gwinn at raytheon.com
Wed Feb 3 00:58:47 UTC 2010


time-nuts-bounces at febo.com wrote on 02/02/2010 07:20:24 PM:

> From:
> 
> Bruce Griffiths <bruce.griffiths at xtra.co.nz>
> 
> To:
> 
> Discussion of precise time and frequency measurement 
<time-nuts at febo.com>
> 
> Date:
> 
> 02/02/2010 07:27 PM
> 
> Subject:
> 
> Re: [time-nuts] Triangle Waves
> 
> Sent by:
> 
> time-nuts-bounces at febo.com
> 
> Magnus Danielson wrote:
[snip]
> > Just a reality check question here... a simple triangle oscillator is 
> > very easily created by two op-amps, one for an integrator and one for 
> > Schmitt trigger operation. If you want better long-term stability open 

> > the loop and insert a 10 Hz from your favourite divider chain of a 
> > trusted 10 MHz or so. Would such a design be limiting your measurement 

> > goals considerable, and would any flaws be reasonably to overcome by 
> > better design?
> >
> > Cheers,
> > Magnus
> >
> For beat frequencies in the 1-100Hz range one only need verify the ZCD 
> jitter and delay variations etc., to within a few nanosec.
> In the short term such jitter tantalisingly close to what a well 
> designed audio oscillator is capable of.
> Unfortunately the trigger jitter in most counters is very large for 
> frequencies in this range so verifying the low jitter of an audio 
> oscillator requires using a ZCD or equivalent.

Would integration of a 50% duty cycle square wave generate an adequate 
triangle wave?  Modern opamps make pretty good low-noise integrators, 
although one would need to use a good integration capacitor to ensure 
linear ramps.

The square wave would come from a simple binary divider chain, which will 
clean many things up and ensure a stable duty cycle, whatever the nature 
of the original signal source.

Joe Gwinn




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