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Circuits Current Sense & Source Low Side Current Sense
Circuits Signal Conditioning Operational Amplifiers (Op Amps) Precision Amplifiers
Circuits Signal Conditioning Operational Amplifiers (Op Amps) Low Bias Current Amplifiers

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Eight Decade Current Sensing Log Amplifier

View Full Size Image View Original Datasheet Eight Decade Current Sensing Log Amplifier

The low pA's of bias current of CMOS amplifiers make them suitable for high input impedance current sensing applications. By taking advantage of the logarithmic relationship of a transistor base-emitter voltage to it's collector current a very wide range of measured input current can be converted to a voltage. In this circuit the input current can span six decades from 10nA to 10mA. The positive tempco resistor compensates for the 0.3%/C tempco of the logging transistors scale factor coefficient (kT/q).



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