light to frequency converter

Hi guys, i currently been working on this sensor TCS230, there is a portion of this sensor where is converts light to frequency, the datasheet is attached, so the
problem is i dont get the theory behind this conversion and through my
research i couldnt find any appropriate findings on this particular part, do
help me please.

 

Photovoltaic output current is directly proportional to illumination. A capacitor charged with constant current will have a constant rate of voltage increase over time. A comparator reading this voltage increase can discharge the capacitor. This makes a ramp-generating oscillator, thereby converting current (therefore light) to frequency. Converting the ramp to a square wave with 50% duty cycle could be accomplished in several ways.