An image sensing system and methods for operating the same are disclosed. An image sensing system includes a plurality of pixel circuits, a multiplexer configured to select one of the pixel circuit and provide analog pixel data without sampling, and a successive approximation register (SAR) analog-to-digital converter (ADC) configured to convert the analog pixel data into digital data. The SAR ADC includes a capacitive digital-to-analog converter (CDAC) configured to convert contents of the SAR into a corresponding analog signal for comparison, by a comparator, with the analog pixel data. The CDAC includes a two-dimensional array of circuit elements. A control circuit in the image sensing system is configured to cause random ones of the circuit elements of the CDAC to be selected for generation of the corresponding analog signal and add a dithering signal so a CDAC output and shuffle a multiplexer switch sequence to improve fixed pattern noise.