System and apparatus for generating ideal rise and fall time

A system for generating a reference transition time, the system comprising:

• a first current source, for providing a first current;
• an adjustable capacitive component, coupled to the first current source, for generating an output signal according to a total capacitance controlled by a comparison signal;
• a signal conversion circuit, coupled to the adjustable capacitive component, for controlling charges stored in the adjustable capacitive component to return to an initial value when a voltage level of the output signal reaches a reference value to generate a periodic signal, rising or falling edges of the periodic signal corresponding to the charges stored in the adjustable capacitive component returning to the initial value;
• and
• a comparison circuit, coupled to the signal conversion circuit and the adjustable capacitive component, for comparing a period of the periodic signal with a reference period of a reference clock signal and generating the comparison signal to adjust the total capacitance of the adjustable capacitive component when the periods are not the same.