Logarithmic current electrometer using light emitting diodes

The limit of low current measurement using logarithmic current to voltage converter is improved by 6–7 orders of magnitude with the use of diodes of large band gap as compared with silicon diodes. Low cost commercially available light emitting diodes (LEDs) have been used for this purpose. A theoretical study and experimental measurement of device constant and reverse saturation currents of the whole class of commercially available LEDs has been carried out. A circuit has been developed which makes use of a new technique for temperature compensation and its performance is compared with the technique in common use. The performance of the amplifier is found to be stable in the temperature range 5–60 ◦C for both polarity of signals from 10−12 to 10−5 A.