A Simple High Accuracy Logarithmic Count Rate Circuit Suitable for Spacecraft Use

Described is a diode-pump type circuit without diodes in the signal path, resulting in a circuit that can be accurately analyzed. The analysis is given, as are plots of various ranges and accuracies. The experimental circuit is logarithmic ±1 per cent over a three decade count rate range throughout the temperature range of -40°C to + 75°C. Power consumption is approximately 25 milliwatts. Variations of the circuit are discussed for adaptation to various system constraints.