International Radiation Detectors, Inc.

Amplifier for the AXUV Series Photodiodes
(MODEL # AXUV100HYB1V/Cu)

General purpose electrometers are extremely sensitive instruments used in the measurement of current generated by the photodiodes. They are commonly used with the AXUV series photodiodes around a synchrotron light source. However, the relatively large size of many commercial electrometers make it difficult to locate them close to the detector. The long interconnecting cables can pick up significant amounts of noise from electromagnetic interference and from mechanical vibration. This problem has been noticed by scientists from several laboratories as evident from the recent literature on the detector/amplifier combinations [1,2]. Reference [1] reports a silicon diode/operational amplifier combination with noise performance comparable with photomultiplier tubes and avalanche photodiodes. Scientists at NIST have demonstrated 14 decades of photocurrent at room temperature using low noise operational amplifiers [2]

The AXUV100HYB1V/Cu is a high vacuum compatible current to voltage converting amplifier that was developed specifically for use with the AXUV100, AXUV20, UVG100 and UVG20 photodiodes. With a standard 10 GΩ feedback resistor detector/amplifier hybrid can be used to measure small photogenerated currents with a resolution of 10 fA and a dynamic range of four orders of magnitude. The V (Variable) descriptor indicates that the 10 GΩ resistor may be replaced to effect the dynamic range.

The AXUV100HYB1V/Cu replaces teflon connecting of the AXUV100HYB wires with copper pins. The alternative configuration allows for vacuum compatible socket connections to be made to the back of the amplifier board. Signal is carried through a shielded twisted pair teflon cable. Power is provided on a pair of unshielded teflon wires.

Fig. 1: The AXUV-100HYB1 Amplifier

Fig. 4 AXUV100HYB1V/Cu electrical schematic
(with 10 GΩ feedback resistor)

References:

[1] R. J. Fonck et.al.
"Low Noise Photodiode Detector for Optical Fluctuation Diagnostics"
Rev. of Sci. Instr. Vol. 63, P. 4924-4926 (1992)

[2] G. Eppeldauer and J. E Hardis
"Fourteen-decade Photocurrent Measurement with Large - area Silicon Photodiodes at Room Temperature"
Appl. Optics, Vol. 30, 3091-3099 (1991)