This work describes a capacitive type touch sensor readout circuit using a current based capacitance-to-time converter with comparator threshold level self-adjustment. The proposed circuit generates an output pulse with duty-cycle corresponding to the panel capacitance variation using a simple switch control block, a current generator, and a comparator. This does not require additional amplifiers and passive capacitors/resistors. As a result, the proposed scheme can lead to small size and low power on-chip solution with fast detection time compared to conventional touch sensor readout circuits. Furthermore, due to the comparator threshold level selfadjustment, the readout circuit is less sensitive to component mismatch and process variations. The readout circuit is implemented using CMOS 0.35 µm technology with core area of 100 µm × 27 µm and power consumption of 52 µW, which can detect the touch panel capacitance ranging from 5 pF to 50 pF.