småsignalmodell

A småsignalmodell, or small-signal model, is a simplified representation of a non-linear electronic circuit or system. It is used to analyze the circuit's behavior for small variations around a specific operating point, typically a DC bias point. By linearizing the circuit's equations around this point, a small-signal model allows for the application of linear circuit analysis techniques. This is particularly useful when dealing with active components like transistors and operational amplifiers, whose behavior is inherently non-linear.

The process of creating a small-signal model involves several steps. First, the circuit is analyzed in its DC operating condition to determine the bias voltages and currents. Then, each non-linear component is replaced by its corresponding small-signal equivalent circuit. For instance, a bipolar junction transistor (BJT) might be represented by its hybrid-pi model, which includes small-signal parameters like transconductance and output resistance. Similarly, a diode might be replaced by a small-signal resistance. AC sources are typically retained, while DC sources are short-circuited.

The resulting small-signal model is a linear circuit that accurately describes the circuit's response to small AC signals superimposed on the DC bias. This allows for the calculation of important parameters such as voltage gain, current gain, input impedance, and output impedance for small AC signals. The validity of the small-signal approximation depends on the magnitude of the AC signals; if the signals are too large, the non-linearities become significant, and the small-signal model may no longer provide an accurate representation.