Hi …….unless the oscillator has a bias / attenuator network internally to shift the region of the varicap’s capacitance/voltage curve the efc affects. That’s often done to modify the linearity of the tuning curve.
It’s pretty simple to check. Put an ohm meter on it and see what it reads. Check on a couple of ranges in case you are forward biasing something. Bob On Nov 7, 2013, at 6:09 AM, Charles Steinmetz <[email protected]> wrote: > Bob wrote: > >> I think I may need to change the LPF feeding the EFC in my GPSDO to get rid >> of dithering jitter. Is there any point in adding a resistor and cap in the >> EFC line, or do I need to go back and change the values in the op-amp >> circuit feeding it? Currently an op-amp directly feeds the EFC pin. I >> guess this boils down to something like: is there any meaningful current >> flow in EFC circuit in this oscillator? Or should I add them but will I >> probably have to change the existing filter, as well? > > Generally, an EFC pin connects internally to one or more varicap diodes, > which by definition must be reverse biased (thus, the only current flow is > the reverse current (leakage) of the diode(s)). There is often an internal > series resistor of 50-100k between the EFC pin and the diode(s). It is > common to use an additional, external series resistor and shunt capacitor, > generally 10-50k and anywhere from 0.01uF to tens or even hundreds of uF, > depending on the application. Of course, this additional pole needs to be > taken into account in the loop stability analysis of the PLL. > > Best regards, > > Charles > > > > _______________________________________________ > 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.
