Sisääntövastus

Sisääntövastus, also known as input resistance, is a fundamental electrical property representing the opposition a circuit or component presents to the flow of alternating current (AC) at its input terminals. It is analogous to DC resistance but specifically applies to AC circuits, encompassing both resistance and reactance. It is measured in ohms (Ω).

The concept of sisääntövastus is crucial when analyzing how a signal source interacts with a load. A high sisääntövastus means the component draws very little current from the source for a given voltage, while a low sisääntövastus indicates it draws more current. This is particularly important in amplifier design, where matching the input resistance of one stage to the output resistance of the previous stage can maximize power transfer or minimize signal loss.

Sisääntövastus is not a single, fixed value for all components. It can vary with frequency due to the presence of reactive components like capacitors and inductors within the circuit. For purely resistive circuits, the sisääntövastus is simply the resistance. In more complex circuits, it is a complex number that includes both a real part (resistance) and an imaginary part (reactance). Understanding sisääntövastus is essential for accurate circuit analysis, impedance matching, and optimizing signal transmission.