digital PFD/divider and analog VCO in PLL??

[zhangjavier]

digital pfd

the output of vco is sin, but PFD and divider are all digital. their input should be square.
is this a contradiction??

 

[biff44]

Jeez, yeah. Someone should invent a circuit that can convert a sine wave into a square wave! Could make a lot of $.

 

[orley]

It's not difficulty!

If you put the divider bewteen the PFD nad VCO, the output of VCO is sine which will input thedivider, then you insert a circuit to make sine to square. Eg.the circuit is a OPA,and the OPA can cut the sine to square,--you may set input dc highly and load resistor(or other active load) small, so the output means square, then add buffers(inverters) to make the outout of OPA to be a ideal square.

Best Regard!