Hi My *guess* would be that magnetic pickup (power lines etc) in the L of the L/R (or LC or even RLC) network would be a difficult problem to address. Big toroidal coils might be one solution to that.
Cost wise the DAC is looking better and better.... Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Magnus Danielson Sent: Wednesday, February 03, 2010 4:02 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Triangle Waves Bruce Griffiths wrote: > Joseph M Gwinn wrote: >>> 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 >> > Yes one shouldn't lose sight of the goal which isnt a perfect triangular > wave, but merely a low jitter one. Indeed. > The major problem is the Johnson noise of the resistors used in the > integrator. > > If for example one uses a simple RC filter using 25k plus 10uF and > drives it with a 10Hz square wave the output noise at dc is about > 20nv/rtHz. > The output slew rate with say a 5V amplitude square wave is about 1V pp > and the zero crossing jitter due to Johnson noise is on the order of 3ns. Hmm... what about an LR replacement of the RC chain over the op-amp? Just a thought. It is a bit uncommon, but is essentially the same in function. Could prove interesting since the LR balance could possibly allow for lower noise selections. Cheers, Magnus _______________________________________________ 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. _______________________________________________ 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.
