In electronics, h-parameters (hybrid parameters or h-parameters) are a set of four parameters that describe the behavior of a linear electrical network, such as a transistor or a two-port network, in terms of voltage and current. These parameters are commonly used in small-signal analysis, which is a linear approximation technique used to analyze the behavior of circuits around their operating points.
The h-parameters are typically denoted as follows:
h<11> (hie): This parameter represents the input impedance of the network when a voltage is applied to the input terminal and the output terminal is open-circuited. It's the ratio of the change in input voltage to the change in input current while keeping the output voltage constant.
h<12> (hre): This parameter represents the reverse voltage gain of the network when a voltage is applied to the input terminal and the output terminal is open-circuited. It's the ratio of the change in output voltage to the change in input current while keeping the input voltage constant.
h<21> (hfe): This parameter represents the forward current gain of the network when a voltage is applied to the input terminal and the output terminal is loaded with a certain impedance. It's the ratio of the change in output current to the change in input voltage while keeping the output voltage constant.
h<22> (hoe): This parameter represents the output conductance of the network when a voltage is applied to the input terminal and the output terminal is loaded with a certain impedance. It's the ratio of the change in output current to the change in output voltage while keeping the input voltage constant.
The h-parameters are particularly useful for analyzing transistor circuits, as they allow you to easily determine how changes in input voltage and current affect output voltage and current. These parameters can also be used to calculate other important characteristics of a circuit, such as voltage and current gains, input and output impedances, and more.
Keep in mind that h-parameters are valid only for linear circuits operating in a small-signal regime, meaning that the changes in voltages and currents around the operating point should be small enough to maintain linear behavior. For large-signal analysis or non-linear circuits, more advanced modeling techniques are needed.