Control circuit for sensing capacitive changes of a touch panel and a method thereof

A control circuit for a touch panel, comprising:

• a signal-detecting circuit for charging a sensing wire of the touch panel to obtain an intensity signal of the sensing wire, wherein the signal-detecting circuit is a capacitance-detecting circuit for providing a power source to charge an equivalent capacitor of the sensing wire, and correspondingly providing the power source having the same magnitude to charge an internal capacitor of the capacitance-detecting circuit so as to obtain the intensity signal,
• wherein the voltage Vout of the intensity signal generated by the capacitance-detecting circuit is expressed by the following formula:
• V
• out
• ≈
• L
• a
• ⁢
• W
• b
• W
• a
• ⁢
• L
• b
• ⁢
• (
• V
• DD
• -
• V
• T
• )
• ⁢
• C
• X
• C
• in which La is the gate length of a transistor a of the capacitance-detecting circuit, Wa is the ate width of the transistor a, Lb is the gate length of a transistor b of the capacitance-detecting circuit, Wb is the gate width of the transistor b, VDD is the supply voltage. VT is the critical voltage of the transistor b, Cx is the sum of the equivalent capacitance of the sensing wire and a stray capacitance of the circuit board of the control circuit, and C is the internal capacitance of the capacitance-detecting circuit;
• an intensity/frequency conversion unit for converting the intensity signal into a frequency signal, the frequency of which corresponds to the level of the intensity signal;
• and
• a frequency-analyzing unit for analyzing the frequency signal to obtain a signal amount of the corresponding sensing wire.