A heating system and a method for heating a battery module are provided. The applications that are installed in an external or embedded storage of the portable device are searched and the usage frequency of each of the applications is obtained, when the portable device is booted or rebooted. The hierarchical chart is updated after filtering criteria are applied, and the display visibility of the nodes are changed based on the filtering results. At least a portion of the image is displayed on a display. Other methods are also presented. In one configuration, a reference transistor in the control circuit controls a current mirrored to a column line, and each pixel sensor in the corresponding column contains a transistor that acts as half of a differential pair when the row containing the pixel sensor is selected.