For ultraviolet limb imaging spectrometers, a system-level design scheme of the imaging circuit featured by analog-digital separation was presented to avoid the CCD output analog signal transferring between the boards and the interference of digital signals to analog signals.As a result, a 2 LSB noise performance of the CCD signal processing circuit is achieved, which is exactly coincident with the noise specification on the Analog Front End(AFE) datasheet. As the CCD57-10 BI AIMO has no anti-blooming structure and its charges will overflow before getting saturated, a concept about the critical blooming electron counts was defined to replace the saturation electron counts. By raising the high level voltage of CCD transfer clock signals to improve the depth of potential well, the critical blooming electron counts are increased from 30×104 to 60×104, which ensures the highest intensity light signal in the designing range to be correctly detected. To take shorter exposure time to expand dynamic range, the idea of multiple charge-dumping was introduced into the design of drive timing. Without sacrificing the dynamic range of the detector, the minimum exposure time is brought down as small as 19 ms, which is almost an order magnitude lower than that of traditional CCD and ensures the system dynamic range design of 105.