Apparatuses and methods for a reference clock-less CMOS image sensor are disclosed herein. An example apparatus may include a controller coupled to an image sensor via a serial bus, and the controller may provide an access burst to the image sensor over the serial bus, the access burst including a plurality of data signals and an associated clock signal, where the associated clock signal is a timing signal for the acquisition of bits of the plurality of data signals. The image sensor may calibrate an internal clock signal in response to a comparison of a number of cycles of the internal clock signal occurring during the access burst to a number of cycles of the associated clock signal occurring during the access burst, where the associated clock signal cycles at a first frequency and the internal clock signal cycles at a second frequency different than the first frequency.