Now you've lost me. What 2.5 MHz synchronizer clock? Everything I have external to the PIC is 10MHz. The PIC is running HSPLL at 40MHz, though I don't think that makes any difference to this.
Bob >________________________________ > From: Bruce Griffiths <bruce.griffi...@xtra.co.nz> >To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency >measurement <time-nuts@febo.com> >Sent: Thursday, February 20, 2014 3:07 AM >Subject: Re: [time-nuts] TIC model > > >R2 is dominated by the adc sample switch on resistance and thus has a >relatively high tempco (~4000ppm/C). >C2 has a relatively low tempco (~100ppm/C or so) > >To reduce the effect of the sample switch on resistance tempco on the >gain tempco of the TIC R1 C1 need to be proportioned so that R2 has >little effect on the gain temcpo. >R1 = 470 ohm, C1 = 1nF (NPO) appears to be about right for a 2.5MHz >synchroniser clock and the PIC you intend to use. > >This should reduce the effect of the sample switch on resistance tempco >by a factor of 10 or more. > >The minimum value of R1 is governed by the output resistance of the >tristate buffer and its tempco. > >Bruce > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.