A Logarithmic Current-to-Voltage Amplifier with High Sensitivity, Stability, and Dynamic Range, Suitable for Field Application

A logarithmic amplifier is described which has a dynamic range of 6 decades of input current (from 10-13 to 10-7 A) while maintaining very good logarithmic response (output voltage deviates less than ±1% from a logarithmic function). A high degree of temperature stability is also achieved (total offset less than ±2% of full scale voltage over ambient temperature range from -10°C to +70°C). It has a usable range (by nonlogarithmic response extensions) to 9 decades. The circuit covers its exceptionally wide dynamic range without range switching. Power requirement is less than 1 W, and the circuit fits ontwo 4 X 4 inch printed circuit boards. It is readily portable and performs well under rugged field conditions, as demonstrated by its successful use in Plowshare nuclear cratering experiments.