How should I interpret these specs? They can't both be correct all the time, right? Looking at for example the CA3140 opamp. the Zin (input impedance) is 1.5T Ohm, yet the input current is 10pA. Solving this for voltage (Ohm's law, 1,5e12 * 10e-12) gives 15 volt, so at that input voltage, both these specs are correct.
- But what happens when you give the opamp 100mV at its input?
- Do I calculate the input current according to the Zin or do I assume that it's 10pA?
Assuming the opamp draws 10pA, the input impedance is now R = U / I = 0,1 / 10e-12 = 1e10 Ohm instead of 1.5e12.