A method for implementing virtual metal fill includes obtaining a layout record for a circuit design, and inserting metal fill data into the layout record based on one or more rules, wherein the metal fill data represents a consolidation of actual metal fill. The aim of the invention is to ensure long-term secure positioning of the sapphire or similar material on the nozzle strip. The column sensing electrodes of sensing cells in the same column are electrically coupled together, and the row sensing electrodes of sensing cells in the same row are electrically coupled together. During the offset-cancel preparation period, the switches SW1 and SW3 are on and the switch SW2 is off.