The present invention provides a signal processing circuit including a control unit, a transmission drive unit, an analog switch array, a signal amplification unit, a detection integration unit that are connected in sequence, and a transceiver antenna connected to the analog switch array. The control unit includes an analog-to-digital converter. The signal processing circuit further includes a level conversion unit arranged between the analog-to-digital converter and the signal amplification unit, the level conversion unit is configured to linearly convert signals received by the transceiver antenna, and transmit the linearly converted signals to the analog-to-digital converter. The signal processing circuit has advantages of low cost, fast handwriting speed, and less cursor wobble. The present invention also provides a position detecting device using the same.