<^< Worksheet: Voltage Gain | Course Index | Output Resistance >^>
The input resistance of an operational amplifier is defined as the ratio of input voltage to input current expressed in ohms. It is often expedient to assume that the input of an operational amplifier is purely resistive though this is not the case at high frequencies where shunt capacitive reactance may become significant. The input resistance of operational amplifiers is very much dependent on the semiconductor technology employed. In practice values range from about 2 MΩ for common bipolar types to over 1012Ω for FET and CMOS devices.
Input resistance is the ratio of input voltage to input current:
RIN = VIN/IIN
where RIN is the input resistance (in Ω), VIN is the input voltage (in V) and IIN is the input current (in A).
<^< Worksheet: Voltage Gain | Course index | Output Resistance >^>