  The capacitance of the charge collection node of a sensor system is an
important parameter for the design of the analog front-end electronics. The
analog front-end of high-granularity sensors like for example hybrid pixel
detectors need to be optimized for timing resolution, power consumption, and
electronics noise - parameters which all depend on the pixel capacitance.
Current pixel detector developments for the HL-LHC upgrade typically use
silicon sensors with a pixel size in the order of $50 \times 50 um^2$ which
have a pixel capacitance of several tens of fF, depending on the sensor
geometry. We have developed a dedicated integrated circuit to be bump-bonded to
a pixel sensor, which enables a precise pixel capacitance measurement by using
charge-based capacitance measurement method. In this paper, we will describe
the measurement method and the implementation of the capacitance measurement
chip (Pixcap65) and show measurement results of a planar pixel sensor whose
pixel capacitance is influenced by variations of the implant geometry.
