I would be pleased to contribute a 100 MHz wenzel onyx for testing if that'd be of value. I don't see myself getting to it anytime soon and this project directly benefits almost half the things on my "never to do but wish I could" list On Sun, Oct 25, 2015 at 7:00 PM Bruce Griffiths <[email protected]> wrote:
> On Sunday, October 25, 2015 09:21:02 AM Charles Steinmetz wrote: > > I wrote: > > >>According to the simulation, the resistor has no effect on the output > > >>amplitude until it is well below 1k ohms > > > > Bruce replied: > > >even 10k increases the output signal amplitude by 130mV or 2.6%. > > >However that is smaller than the tilt/sag in the high level output due > to > > >feedthrough via Cbe of the input transistor when it is off. > > > > Bruce is correct, although I don't consider 130mV to be a significant > > effect on a 5v logic level. My fault, I guess, for saying "no" > > effect instead of "no significant" or "no material" effect. > > > > But, do we really need to dispute every insignificant, niggling > > little detail like this? Even in science, there must be *some* > > allowance for the use of everyday language instead of requiring > > absolute explicit clarification of every possible point, or all > > communications would be unbearably tedious from all of the > > qualifications. I say this as someone who is often criticized for > > overclarifying to the point of being pedantic and tedious. > > > > There was simply no need, nor excuse, for the prior (incorrect) > > suggestion that a resistor to ground from Point "A" would not be > > effective in canceling the small asymmetry of the circuit, OR for the > > suggestion that such a resistor would be a useful means to adjust the > > output amplitude (this because of (i) the concomitant ill effect on > > symmetry and (ii) the much more direct and efficacious means of > > achieving the result by adjusting R6 or R1 and R2). > > > > Best regards, > > > > Charles > > > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-in/mailman/listinfo/time-nuts and follow the > > instructions there. > Charles > > There was no such suggestion, merely a note that the amplitude was also > affected by this. This effect is important in that its probably advisable > to > ensure that the input protection diodes of any gate being driven by the > output don't enter into conduction (I discovered that at least for the > 74HC04 that the propagation delay jitter increased dramatically once the > input protection diodes began to conduct). Thus an increase in output > amplitude by a few hundred mV could be detrimental to the performance > of the driven logic device. > > Whilst the symmetry adjustment effect is real its actually achieved by > adjusting the ratio of the emitter currents of the 2 transistors (its not a > threshold effect due to Vbe changes -they are too small but an adjustment > of the differential switching delays of the 2 transistors). > Consequently adjusting the ratio of emitter currents of Q1 and Q2 is best > made via a pot (200 ohm??) connected between the upper ends of R1 and > R2 (reduce R1 and R2 to 910 ohm) with its wiper connected to the C5, C6, > C7, R7 node. > Adjusting the wiper position has very little effect (tens of mV) on the > output amplitude whilst allowing adequate range of adjustment of the > output signal duty cycle. > > Adjusting the value of R6 can be counter productive in that it spoils the > match to a 50 ohm load achieved via simple 2:1 (turns ratio) stepdown RF > transformer for the purposes of measuring the PN of the circuit. > > Bruce > _______________________________________________ > 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.
