The present invention relates to an optical biometric sensor (100) comprising: an image sensor (302) comprising an array (301) of photodetectors (304), wherein for acquiring sensing signals, the image sensor is controllable to sequentially start exposure of subsets (306, 308, 309) of photodetectors; and a timing circuitry (310) configured to control the start of exposure of a subset of photodetectors based on a present data transfer capacity on a data transfer bus (312) configured to transfer data indicative of the acquired sensing signals from the optical biometric sensor to a host device (314).