Picoammeter circuit

  
The circuit uses the exceptionally low input current (O.lpA) of the CA3420 BiMOS op amp. With only a single 10 megohm resistor, the circuit covers the range from ±50 pA maximum to a full-scale sensitivity of ±1.5 pA.
Picoammeter circuit - schematic

Using an additional CA3420, a low-resistance center tap is obtained from a single 3-volt lithium battery.




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