Opampin

Opampin is an informal term sometimes used in electronics to refer to the input side of an operational amplifier, especially the node where the input signal is applied. It is not a standard designation in datasheets or formal specifications; official terms are the non-inverting input and the inverting input, along with the input pins and associated input impedance.

Electrical characteristics at the opampin node vary by technology and part, but several features are common. The inputs present a very high impedance, typically spanning from kiloohms to gigaohms, which minimizes signal loading. Input bias currents range from picoamperes to microamperes depending on the topology (for example, FET-input devices tend to have lower bias currents than bipolar ones). Input offset voltage can range from microvolts to millivolts, affecting accuracy. The input common-mode range is determined by the supply rails and the stage design; rail-to-rail types extend closer to the supply limits. Input capacitance, often tens to hundreds of picofarads, interacts with surrounding circuitry and can influence high-frequency behavior.

In circuit operation, the opampin node is typically connected to a feedback network that sets closed-loop gain. Properly designing around this node requires attention to common-mode excursions, input loading, and stability considerations, since stray capacitance or leakage can alter performance, especially at high speeds. Protection diodes, biasing schemes, and proper layout help maintain predictable behavior.

Because opampin is informal, engineers should rely on standard specifications for the actual part using electrical term names like non-inverting input, inverting input, input impedance, bias current, and offset voltage to avoid ambiguity. See also: operational amplifier, non-inverting input, inverting input, differential amplifier.