SiGe BiCMOS technology can be used to produce ultra-fast, low-power silicon pixel sensors that provide state-of-the-art time resolution even without internal gain. The development of such sensors requires the identification and control of the main factors that may degrade the timing performance as well as the characterisation of the dependance of the sensor time resolution on the amplifier power consumption. Measurements with a Sr-90 source of a prototype sensor produced in SG13G2 technology from IHP Microelectronics shows a time resolution of 140 ps at an amplifier current of 7 mu A and 45 ps at a power consumption of 150 mu A. The resolution on the measurement of the signal time-over-threshold, which is used to correct for time walk, is the main factor affecting the timing performance of this prototype.