I am working on a variable speed motor drive using an 8052 to compute the control signals. Supply syncronisation is being obtained using a KA311 comparator fed from a step down transformer connected to one phase. Unfortunately this method of generating the reference signal is not accurate enough for higher switching frequencies as any noise on the input sinewave affects the point of zero cross.

If anybody has any ideas on which is the best way of creating a clean reliable reference signal, i would appreciate it.

Thanks

Konrad