Question

[h] = ?

I had been asked this question in a job interview.

My question is based upon Two Port Network in section EDC Overview of Electronic Devices & Circuits

Answer 1

The [h] matrix in a two-port network, also known as the hybrid parameters, relates the input voltage and output current to the output voltage and input current. The [h] parameters are a set of coefficients that describe how the currents and voltages at one port affect the voltages and currents at the other port.

The general form of the [h] matrix is:

[V1I2]=[h11h12h21h22][I1V2]\begin{bmatrix} V_1 \\ I_2 \end{bmatrix} = \begin{bmatrix} h_{11} & h_{12} \\ h_{21} & h_{22} \end{bmatrix} \begin{bmatrix} I_1 \\ V_2 \end{bmatrix}[V1​I2​​]=[h11​h21​​h12​h22​​][I1​V2​​]

Where:

• V1V_1V1​ and I1I_1I1​ are the input voltage and current, respectively.
• V2V_2V2​ and I2I_2I2​ are the output voltage and current, respectively.

The corresponding equations are:

V1=h11I1+h12V2V_1 = h_{11} I_1 + h_{12} V_2V1​=h11​I1​+h12​V2​ I2=h21I1+h22V2I_2 = h_{21} I_1 + h_{22} V_2I2​=h21​I1​+h22​V2​

Explanation of Parameters:

• h11h_{11}h11​: Input impedance with the output voltage held constant (i.e., the ratio of the input voltage to the input current when the output voltage is zero).
• h12h_{12}h12​: Reverse voltage gain with the output current held constant (i.e., the ratio of the input voltage to the output voltage when the input current is zero).
• h21h_{21}h21​: Forward current gain with the output voltage held constant (i.e., the ratio of the output current to the input current when the output voltage is zero).
• h22h_{22}h22​: Output admittance with the input current held constant (i.e., the ratio of the output current to the output voltage when the input current is zero).

Key Points:

• The [h] parameters are often used in amplifiers and transistors, especially in situations where both voltage and current relations are important.
• These parameters are particularly useful for analyzing networks where the hybrid (combination of impedance and admittance) characteristics are of interest.
• The [h] matrix allows for the representation of both voltage and current behaviors at the input and output ports simultaneously.

Summary:

The [h] parameters matrix provides a compact and useful representation for analyzing two-port networks, particularly where both voltage and current relationships need to be considered. The hybrid parameters are widely used for describing the behavior of amplifiers and other active devices.