From: Dr Bruce Griffiths <[EMAIL PROTECTED]> Subject: Re: [time-nuts] Allan Deviation -> continuing saga... Date: Sun, 29 Oct 2006 10:35:44 +1300 Message-ID: <[EMAIL PROTECTED]>
Good Morning Bruce! > Comparators are fine with a good layout. As you sharpen up the rise-times, layout becomes more and more important. > If the input signal is low noise and has a sufficiently high slew at the > switching threshold hysteresis is unnecessary. In this case we are talking about a 10 MHz sine(like) and fairly good amplitude, so the slew-rate should be good, just in need of the slew-rate boost prior to hitting those F161s. > Older ultrahigh speed TTL comparators like the AD9696 and AMD686 have an > output stage that is inherently unstable in the transition region. > If the input to the output stage remained too long in this region the > output stage oscillates. OUCH! Thanks for the heads up! > Even these work well with a good layout and a nice clean low noise high > slew rate input signal. > Hysteresis is mandatory when using these comparators with low slew rate > inputs to maintain stability. Indeed. However, hysteresis is unfortunatly mistaken for being a cure for noise-induced jitter. It ain't. Increased gain prior to the hysteresis is. Cheers, Magnus _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
