Tektronix - P7380A GHz Tektronix created the Z-Active probe. 
Z-Active Differential Probe 8 GHz
Tektronix created the Z-Active probe architecture and set the industry benchmark for signal fidelity. Tektronix active probe architecture preserves high bandwidth while providing improved connectivity with low loading and low noise. The Z-Active architecture is a hybrid approach composed of a distributed attenuator topology feeding an active probe amplifier. The Z-Active probes use a tiny passive probe tip element that is separate from the amplifier, extending the usable reach of the probe.