Hi If that's a concern, use a 74ACT part
Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Jerry Mulchin Sent: Friday, May 18, 2012 3:20 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Buffering a PPS signal Be careful that you use the proper logic device for the GPS 1PPS output. An 74AC device has a minimum HIGH input logic level of 2.1 volts when running with a 3.0 volt VCC, and 3.65 when running at 5 volt VCC. A GPS receiver running at 3.3 volts may be on the edge. Consider using a 74F part instead as it has a lower HIGH input requirement when running a 5 volt VCC than a 74AC. Jerry At 11:50 AM 5/18/2012, you wrote: >On 05/18/2012 07:24 AM, Bob Camp wrote: >> Hi >> >> For a 50 ohm buffer, you probably want something like 200 ohms in series >> with each output (4 buffers) or 400 ohms (8 buffers). > >It may be worthwhile considering the gate output impedance as well. For >example, for 5V AC logic driving a 50 ohm line the initial edge from the gate is >about 4V - which implies a Zo of about 13 ohms. A 50 ohm buffer with 4 gates >would therefore use 187 ohms series resistors. > >There is an app note attached here that discusses this: > > http://c-c-i.com/node/107 > >-- >Bob Smither [email protected] >========================================================================== >A well regulated Militia, being necessary to the security of a free State, >the right of the people to keep and bear Arms, shall not be infringed. > -- Second amendment to the Constitution of the united States >========================================================================== >Circuit Concepts, Inc. 281-331-2744 > > >_______________________________________________ >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. Jerry Mulchin _______________________________________________ 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.
