Remodeling light emitting diode in low current region

A general expression is proposed for the current-voltage (I-V) characteristics of junction diode by which it is possible to determine forward voltage across diode at actual current and temperature. Expressions fur the band gap and temperature coefficient of junction voltage based on the experimental measurements are also presented. The expressions include only experimentally obtained and derived values. These expressions have been used to check the performance of logarithmic amplifier using light emitting diode (LED) as a feedback clement, at different temperatures. Further, it has been shown that it is possible to predict the behavior of a logarithmic amplifier without temperature compensation techniques within 5% accuracy for the current range 10/sup -12/-10/sup -5/ A and for the temperature range -5/spl deg/-60/spl deg/C. The alternative could be the use of temperature compensation circuitry which may make electrometer circuit more complex. The proposed scheme is useful in applications where it is difficult to incorporate temperature compensation technique and space and power are at premium.