Hi John: I think you mean by "-- paralleling several sections of a 74AC04 hex inverter through 47 ohm resistors" directly connecting the outputs then using a series 47 Ohm resistor. But the post by Normand makes the good point that by using a seperate resistor on each gate the loading on the gate is reduced. So I could use a single 74AC04 chip with 150 Ohm resistors on each gate. I'll try that when I'm finished reading the mail.
Have Fun, Brooke John Ackermann N8UR wrote: >Brooke Clarke wrote: > > >>Hi: >> >>I've got the TVB 1 PPS PIC circuit working and would like to add an >>output IC to drive 50 a couple of Ohm cables. >>Need two outputs, the normal 1 PPS and also the 10 kHz output since I >>think it would work with the SRS app note for making 1,000 TI >>measurements in one second to better see small offsets. >> >>I seem to remember that there may be an internal resistance already in >>some chips so putting a 47 or 50 Ohm resistor in series may result in an >>impedance above 50 Ohms. Any thoughts? >> >>Thanks, >> >>Brooke Clarke >> >> >> > >Hi Brooke -- > >The circuit I use is stolen from Tom Clark's TAC -- paralleling several >sections of a 74AC04 hex inverter through 47 ohm resistors. For the >current TADD projects, I'm using three sections that way, so each chip >gives me two outputs, and I use a 47 ohm SIP resistor pack to keep the >board space down. > >Tom came up with the 47 ohm value (though IIRC he used four sections in >parallel) based on compromising for maximum voltage into a 50 ohm >termination, and best rising edge. > >The 74AC chips don't have internal source resistors, but I think some of >the op amp distribution amp chips might. For square waves at these >frequencies, I'd use 74AC parts over an analog circuit. > >John > > >_______________________________________________ >time-nuts mailing list >[email protected] >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > > -- w/Java http://www.PRC68.com w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml http://www.precisionclock.com _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
