A method and circuit generates a sampling clock signal that digitizes an analog video signal. The sampling clock signal is generated by a clock divider coupled to the horizontal synchronization signal of the analog video signal. A divisor calculator calculates a divisor for the clock divider to control the frequency of the sampling clock signal. Specifically, the divisor calculator selects an initial divisor for the clock divider. Then the divisor calculator calculates a new divisor based on the target pixel value provided by a mode detector and the measured pixel value from a counter. Some embodiments of the present invention fine tune the frequency by testing other possible divisors with a plurality of different phases. In addition, some embodiments of the present invention calibrate the phase of the sampling clock signal to generate a phase shifted sampling clock signal.