[time-nuts] Triangle Waves

Bob Camp lists at cq.nu
Wed Feb 3 01:53:05 UTC 2010


Hi

At least the last time I tried it, the filter a square wave / integrate based on a square wave approach both appeared to give performance that was inadequate. Simply put, the triangle wave should give *better* performance than a similar wave generated off of a pair of good oscillators. That was not the case. Could there have been errors made - sure. Exactly what did I do - long time ago, details are in a log book that probably doesn't even exist any more. 

Ideally the signal source would be much better than the limiter I'm trying to test. If I want to verify a 10 ns limiter, a triangle wave good to a ns or so would be a nice thing to have. It would also be nice to easily verify that device. The objective is a quick test of a limiter rather than the world's best low frequency R-C oscillator. That of course assumes I can womp up the DAC gizmo easily.

Bob


On Feb 2, 2010, at 7:58 PM, Joseph M Gwinn wrote:

> 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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