# Input Bias Current

The inputs should have an impedance of infinity, meaning absolutely no current flows into them. However, this is not actually the case. The amount of current that flows through the op-amp input is called the input bias current.

The input bias current is the DC current required by the inputs of the amplifier to properly operate the first stage. By definition, the input bias current is the average of both input currents.

Electronic Devices : Conventional Current Version, 9th Edition by Thomas L. Floyd

The input offset voltage

is a parameter defining the differential DC voltage required between the inputs of an amplifier, especially an operational amplifier (op-amp), to make the output zero (for voltage amplifiers, 0 volts with respect to ground or between differential outputs, depending on the output type).^{[1}

An ideal op-amp amplifies the differential input; if this input difference is 0 volts (i.e. both inputs are at the same voltage), the output should be zero. However, due to manufacturing process, the differential input transistors of real op-amps may not be exactly matched. This causes the output to be zero at a non-zero value of differential input, called the input offset voltage.