A novel high-impedence probe for multi-gigahertz signal measurement

This paper describes a novel high-impedance hand-held probe based on electro-optic sampling (EOS) for multi-GHz signal measurement of on-board circuits. The probe head and detection optics are assembled into a compact probe module. The probe head consists of a metal needle tip and an EO material. The top of the needle is bonded to the EO material. When the needle makes contact with the signal line of a circuit under test, the signals are measured by detecting the polarization change of laser pulses that propagate through the EO material. The effective 3-dB down bandwidth of the EOS high-impedance probe is 10 GHz. The voltage sensitivity is 0.5 mV/√Hz. The input resistance and capacitance are >100 MΩ and <0.2 pF, respectively. The probe head is very durable and is not susceptible to electrostatic discharge. The probe has been successfully applied to measure multi-GHz signals of on-board communication IC´s