Bob Camp wrote: > Hi > > A very common approach, that also takes care of a few other issues is to > simply declare the upper and lower 10% of the EFC range to be "out of > bounds". Any time the PLL gets into those regions declare it to be > unlocked. Some people use a lot less than 10%, but then find out that > their detector does not quite make it to (say 99%) in all cases. > > The other case you need to worry about with an XOR is total loss of one > input. The detector output will go to center scale and just sit there. > There is nothing you can do on the output side to catch that condition. > You can either detect loss of input directly ( = measure input amplitude) > or you can put in a couple of flip flops to figure out when it happens ( = > put in a sequential detector). > > Bob
When I worked for Zeta Labs building synthesizers in the 1970's, we used this approach in virtually 100% of our products. As Bob pointed out, it is not easily fooled by any likely conditions. And it is simple (just a window comparator). We used to get a dual op amp and use one for the loop filter and the other as a comparator. The one case I am aware of where it can be fooled is if the loop is oscillating. Also, if you are using a mixer for a phase detector, the loop can false lock under some error conditions. Rick Karlquist N6RK _______________________________________________ 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.
