[email protected] wrote on 02/02/2010 08:19:26 PM: > From: > > Bruce Griffiths <[email protected]> > > To: > > Discussion of precise time and frequency measurement <[email protected]> > > Date: > > 02/02/2010 08:20 PM > > Subject: > > Re: [time-nuts] Triangle Waves > > Sent by: > > [email protected] > > Joseph M Gwinn wrote: > > [email protected] wrote on 02/02/2010 07:20:24 PM: > > > > > >> From: > >> > >> Bruce Griffiths<[email protected]> > >> > >> To: > >> > >> Discussion of precise time and frequency measurement > >> > > <[email protected]> > > > >> Date: > >> > >> 02/02/2010 07:27 PM > >> > >> Subject: > >> > >> Re: [time-nuts] Triangle Waves > >> > >> Sent by: > >> > >> [email protected] > >> > >> 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, whateverthe nature > > of the original signal source. > > > > Joe Gwinn > > > > > The integration function requires a low frequency cutoff (either a > servoloop or a resistor shunting the integration capacitor) to avoid > integrator saturation. > This inevitably distorts the triangle wave, however it should be > possible to reduce the triangular wave distortion by predistorting the > integrator input current.
Yes, there would need to be some kind of drift compensation (I favor a opamp servoloop), but given that we are trying to measure ZCD jitter (versus long-term wander), isn't this good enough? The distortion will be small and stable, and so will not cause jitter. Joe Gwinn _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
