Wearable device refers to a device that is always in contact with the body beyond the carrying smartphone. For wearable applications, flexibility is important, which need the integration of the circuit on a substrate. With the discrete devices, it is difficult to bend.

In wearable device, information should be displayed. For the display, drive circuit is necessary. With a battery, we need some boost up circuit such as charge pump for driving of the display. The charge pump need clocks which should be supplied by separate source. In this paper we embedded the clock generator in charge pump circuit.

Charge pump are used in almost all mobile devices and provide a stable output voltage under unstable power condition. Among several types of charge pumps, Dickson type charge pump has been used widely in traditional industrial applications.

In the charge pump circuit, two square waves are alternately applied. At the first stage, the capacitor is charged equal to the supply voltage. In the second stage, the circuit is connected in series with the power supply and the load.

Finally, the voltage across the load increases to twice the sum of the supply voltage and the capacitor voltage. Figure 1 shows proposed charge pump circuit with embedded clock generator and the output voltage of it. The circuit that generates the clocks CK and CKB is necessary for driving the charge pump circuit. The clock generator has the same configuration as the RC oscillator and alternately outputs square wave of 1.5 V.

As shown in Fig. 1, the output voltage is about 6 V when the input voltage is 1.5 V. The output voltage increases linearly with respect to the input voltage. The output voltage variation according to the number of TFTs are also investigated. As the number of TFTs increases, the output voltage increases.