Patent ID: 7436393

Claim:
A touch panel for a display device, comprising: a resistive-type touch panel arranged above the display device; an electromagnetic (EM)-type touch panel arranged below the display device; and a first driving part to drive the resistive-type touch panel, wherein the first driving part generates voltages corresponding to coordinates of a location of an object contacting the touch panel using potential gradients generated across substrates of the touch panel, wherein the electromagnetic (EM)-type touch panel includes: a sensor board including a plurality of antenna coils; a select circuit for selecting one of the plurality of antenna coils; a transmitting circuit for successively applying an AC signal to the selected antenna coil selected by the select circuit to generate an electromagnetic field from the selected antenna coil; a stylus pen generating an induction voltage from the electromagnetic field and discharging the induction voltage to excite the selected antenna coil so that the selected antenna coil generates a received signal; a receiving circuit amplifying and filtering the received signal and outputting a filtered signal; a connection switching circuit for alternately connecting the select circuit to the transmitting circuit and the receiving circuit; and a processing circuit for controlling the select circuit and the connection switching circuit, and detecting a location of a contact point of the stylus pen from the filtered signal, wherein the transmitting circuit includes: an oscillator generating a clock pulse; a frequency divider dividing the clock pulse into first, second and third frequencies; a first NAND gate for calculating the second and third frequencies; a second NAND gate for inverting a signal outputted from the first NAND gate; a driving circuit converting a signal outputted from the second NAND gate to an average signal and transmitting the average signal to the selected antenna coil through the connection switching circuit and the select circuit; and an EXOR gate calculating the first and second frequencies, wherein the receiving circuit includes: an amplifier amplifying the received signal from the selected antenna coil and outputting an amplified signal; a first phase detector receiving the second frequency and the amplified signal from the frequency divider and the amplifier, and generating a first inverted signal; a second phase detector receiving a signal from the EXOR gate and the amplified signal from the amplifier, and outputting a second inverted signal; a first low-pass filter converting the first inverted signal to a first average signal and outputting the first average signal to the a processing circuit; and a second low-pass filter converting the second inverted signal to a second average signal and outputting the second average signal to the processing circuit.