Photoconductive sampling with an integrated source follower/amplifier

Abstract

A hybrid, optoelectronic sampling circuit based on a photoconductive switch and a junction-field-effect-transistor (JFET) source follower/amplifier has been demonstrated to have picosecond response, high-sensitivity, absolute-voltage capability, and a very high impedance. The distributed capacitance of the electrical measurement system is reduced to the gate input capacitance of the JFET, and the conventional photoconductive current measurement is transferred into an absolute voltage measurement. Gating measurements with an improvement of 150 times in output voltage over unamplified photoconductive gates have been made using only 10 μW of average optical power. The effective on-state resistance of the photogate has also been increased by more than 150 times, indicating that a photoconductive probe with very low invasiveness may be produced.