Circuit to measure load currents of less than 100 uA

[klystron]

I need a circuit that can measure load currents of less than 100 uA (with a resolution of 10 uA)
The circuit must have a voltage drop of less than 10 mV

 

[Davood Amerion]

for current measurement usualy we use one resistor which is series with output.
Then measure voltage between 2 terminal of resistor.
For your specification, you must use one opamp to amplify resistor voltage.
For resistor value > 10mV/100uA = 100 ohm
op-amp gain > [desiered output voltage ] / 10mV