Hi My main point is that a +22 dbm (or even 16 dbm) OCXO is a *very* rare item. If your signal generator is set to +22 dbm … shame on you. If the part can do well over +7 to +13 dbm, that will cover the vast majority of the 10 MHz oscillators / signal sources out there.
Bob > On Jan 19, 2018, at 8:51 PM, Bruce Griffiths <bruce.griffi...@xtra.co.nz> > wrote: > > Even the modern PICs spec 50mA max input currents. > Simulation indicates 20mA peak diode currents without the 330 ohm resistors > for a 2V pp input, even more for higher input signal levels. If one can > guarantee that input is around 1V pp then the extra diodes and resistors > aren't required. If its possible that an input of 16dBm or more may be used > then the extra diodes and resistors are required. I simulated the circuit for > inputs up to +22dBm. > Current flowing in the IC protection diodes can degrade the timing jitter > substantially (tens of picosec for HCMOS). > > Bruce >> On 20 January 2018 at 14:34 Bob kb8tq <kb...@n1k.org> wrote: >> >> >> Hi >> >> Unless you really beat on the thing for days on end, you can do without the >> 330 ohm and 100 ohm >> resistors (along with the two diodes). Most modern gates have pretty robust >> protection diodes. The >> source impedance is high enough after the transform that the available >> current is pretty low. On a >> NC7SZ125 the negative diode is rated for 50 ma max and the positive diode is >> rated for 20 ma >> >> Some math: >> >> If the two 1K’s properly terminate the circuit, you have a 250 ohm source. >> (500 ohm load and 500 ohm >> transformed from the sine input). A 1V overdrive (1/2 V + and 1/2 V -) will >> put 2 ma into the diodes on the >> peaks. The more likely case is that the negative is hit a bit harder. The >> bias is most likely a bit below >> 1/2 Vcc for best symmetry. >> >> None of this is to say you *should* hit the diodes. No matter what sort they >> are, the performance will >> degrade a bit when you do. How much is of course a “that depends”. Most of >> us are not driving the >> gate with a -180 dbc/Hz source and expecting -177 out of the gate. >> >> Bob >> >>> On Jan 19, 2018, at 8:14 PM, Bruce Griffiths <bruce.griffi...@xtra.co.nz> >>> wrote: >>> >>> Something like the attached circuit is suitable for driving the MCU clock >>> input directly. >>> The diodes should be schottky signal diodes like the 1N5711 series. The >>> series resistors limit the diode peak current and the CLK input protection >>> network current. It should work with inputs from 1V pp to 8Vpp. If SMT >>> components were used it should all fit on a DIP compatible daughter board. >>> >>> Bruce >>>> On 20 January 2018 at 12:37 Bob kb8tq <kb...@n1k.org> wrote: >>>> >>>> >>>> Bob >>>> >>>> With a 1V p-p sort of output, a simple matching network will get you into >>>> the 4 to 6V p-p range. >>>> Drive that into a 5V compatible CMOS gate and move on …. If you have a >>>> super hot output, put >>>> a 3 db pad on it. >>>> >>>> Bob >>>> >>>>> On Jan 19, 2018, at 5:40 PM, Tom Van Baak <t...@leapsecond.com> wrote: >>>>> >>>>>> Tom >>>>>> What's the input signal amplitude? >>>>>> What's the desired output signal (eg 5V CMOS, 3.3V CMOS etc)? >>>>>> Bruce >>>>> >>>>> It's for a typical 5 or 10 MHz OCXO / Rb / Cs with sinewave output; say, >>>>> 1 Vpp. The output should be 3.3 or 5 V depending on what the MCU needs. >>>>> It doesn't have to have stunning performance: think breadboard, PIC, >>>>> Arduino sort of stuff. I was looking for something in a PDIP-8 package; >>>>> the same as all the picDIV or picPET chips I use. That's why older parts >>>>> like µA9637 / DS9637 came to mind. >>>>> >>>>> /tvb >>>>> >>>>> _______________________________________________ >>>>> 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. >>>> >>>> _______________________________________________ >>>> 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. >>> <PIC_CLK_Network.gif> >> _______________________________________________ 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.
