Sensitivity improvement of an electro-optic high-impedance probe

This paper describes techniques for improving the electro-optic (EO) high-impedance probe for measuring gigahertz signals of on-board circuits. Higher sensitivity is achieved by decreasing the half-wave voltage of the EO crystal in the probe head and by increasing the laser power. To decrease the half-wave voltage, we employ Bi/sub 12/TiO/sub 20/ a newly developed crystal with a larger EO coefficient, and a 1.3-/spl mu/m Fabry Perot (FP) laser diode instead of a 1.55-/spl mu/m distributed feedback (DFB) laser diode. To increase the laser output power, the sampling rate is increased by using a specially-designed laser driver unit. These techniques improve the total voltage sensitivity of the probe system 3.6 times compared to our previous system. This directly leads to a more than one order reduction of signal acquisition time. Moreover, these techniques make the probe system cost effective because they eliminate the need for expensive optical components.