Stability and error analysis of the LED-logarithmic electrometer

Theoretical analysis of the stability and error in the LED-logarithmic electrometer is presented. It has been shown that a resistance in series with the log element improves the response by a factor of 7 at 1pA. Error analysis of the electrometer, involving mainly device parameter sensitivity, is also presented. It has been found that variation in temperature and change in value of the device constant are more important factors than other device parameters in influencing the variation in the output voltage. An eight-decade temperature compensated LED-logarithmic electrometer is designed for the measurement of low currents from 1pA to 0.1mA and has been tested for its performance in the temperature range of –20 to 70°C.