The ability to perform noninvasive logic analysis at the internal points of integrated circuits is crucial in the design and test of advanced microelectronics. We present a noncontact scanning probe technique for extracting high-frequency digital patterns at internal points of an integrated circuit. The digital waveforms are determined by sensing the localized electrostatic force between a small probe and point on the circuit being measured. The force is monitored by detecting the deflection of the probe using a fiber-optic interferometer. The bandwidth of force measurements made using proximal probes are typically limited by the mechanical frequency response of the probe. In the presented instrument high-frequency bit-by-bit digital pattern measurements are enabled by using a pulse sampled heterodyne technique. In conjunction with a nulling approach, the technique is capable of measurements without complex calibration or probe positioning, and can be performed over passivated structures. A simple procedure is also presented which corrects errors due to nonidealities of the pulse sampling waveform. Using a probe with a kHz resonant frequency, Mbit/s patterns have been measured. Errors due to coupling from adjacent signal lines and due to surface charge effects are examined.