power factor calculation using PIC

i m working on digital power factor meter using Pic microcontroller.i m having a problem in finding a phase difference beteen voltage and current signal.
can anyone help me to design a circuit that can measure phase difference between voltage and current or anyone know about any IC for taht purpose

Have a read of An939 from Microchip. It should give you some ideas.

Mike.

It should be fairly easy, you shouldn't need the phase angle. Sample the signal at two times the maximum harmonic of interest and perform some simple waveform arithmetic on it.

Multiply the voltage by the current for each sample and work out the average power over a few cycles; this will give you the true power being dissipated.

Work out the average voltage and current and multiply them together; this will give you the apparent power.

If you know the apparent power and the real power then calculating the power factor is pretty simple.

If you really want the phase angle then you can calculate that by looking at the time difference between the peak current and voltage. The problem is that many loads have a poor power factor because they don't draw a sinusoidal wave form so the phase difference isn't always very meaningful.