# LTSpice Has bizzare results for high input impedance devices

While simulating with LTSpice I discovered the simulator gives milliamps of inverting and non-inverting terminal current in op amps and also the same thing for MOSFETs, milliamps into gates. Here is a simple circuit demonstrating the current into a non-inverting terminal with an op amp. I will also put down that I measured only nanoamps of current into op amp inverting and non inverting terminals and also MOSFET gates in Multisim to verify that LTspice is incorrectly giving results, which leads me to believe LTSpice is seriously flawed and this should be reported to developers. Is this normal or is it a bug which should be reported to developers?

Another circuit

• So what's your question? Commented Jan 30, 2018 at 1:46
• @user33915 Why would you imagine that an opamp has zero (very low) input current when the voltage difference between the inputs is 3 V???? Try arranging things so that both inputs are at 3 V and THEN check the input currents.
– jonk
Commented Jan 30, 2018 at 1:49
• @user33915 1 V is still just as bad. Linear Technology's LT1001 and LT1002 are bipolar opamps. I suppose you have no idea how a bipolar opamp is designed to work? If you want low currents, you MUST keep the differential between the two inputs well under 100 mV and preferably only a few mV, if possible. Try a 30 mV difference, for example.
– jonk
Commented Jan 30, 2018 at 2:20
• @user33915 These things use diff-pairs. Examine Figure from page 167 of a book by Abraham Pressman. Note the range of differences allowed for? And if you look over that nice picture, you'll see that $\pm \:30\:\text{mV}$ is about all you want to allow. This is not a problem with LTspice. This is a user problem. Totally different kind of bug.
– jonk
Commented Jan 30, 2018 at 2:25
• AFAIK LTSpice has realistic device models. A theoretical ideal op-amp draws no current but it is not simulating a theoretical ideal op-amp, it's simulating a LT1002. Commented Jan 30, 2018 at 3:25