This paper presents a CMOS readout circuit to achieve a random method to open the window.The method is achieved by way of decoder, shift registers with the traditional random window readout circuit, this method has the advantage of simple circuit structure, layout, the chip area occupied by small, low power consumption, user co-operation of the Spirit .This paper describes the use of random windows Decoder circuit design and principles of analysis and the corresponding simulation waveforms, the last part of the layout of the design were introduced.