A method and apparatus for performing on-chip voltage sampling of a weakly-driven node of a semiconductor device are disclosed. In some embodiments, the node is a floating node or is capacitively-driven. In some embodiments, it is involved in proximity-based communication. Sampling the node may include isolating the signal to be sampled using a source-follower amplifier before passing it to the sampling circuit. Sampling the node may include biasing the node to a desired voltage using a leaky transistor or other biasing circuit. In some embodiments, the biasing circuit may also be used to calibrate the sampler by coupling one or more calibration voltages to the node in place of a biasing voltage and measuring the sampler output. The sampler may be suitable for sub-sampling high frequency signals to produce a time-expanded, lower frequency version of the signals. The output of the sampler may be a current communicated off-chip for testing.