Touch processor circuit and touch screen system performing analog-to-digital conversion of two steps

A touch processor circuit includes a capacitance-to-voltage converter and an analog-to-digital converter. The capacitance-to-voltage converter converts an input signal transmitted from a touch sensor into a conversion signal corresponding to a capacitance of the touch sensor. The analog-to-digital converter digitizes the conversion signal transmitted from the capacitance-to-voltage converter and generates a digital value. The analog-to-digital converter includes a first converter, a second converter, and a combination logic circuit. The first converter calculates upper bits of the digital value based on the conversion signal during a first time period. The second converter calculates lower bits of the digital value based on a residue component signal transmitted from the first converter during a second time period. The combination logic circuit combines the upper bits and the lower bits and generates the digital value.