John Ackermann N8UR wrote: > 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
I don't think I can post them until later today or tonight, but I recently took some photos of the TADD-3 rising edge, using the parallelled 74AC04s, on a 400MHz scope. I don't recall the exact value right now, but the risetime is well under 5ns, and the high state is more than 3 volts. John _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
