Design Considerations of Junction Transistors at Higher Frequencies: Based upon an Accurate Equivalent Circuit

The analytical solution of the diffusion equation has been used to construct an accurate equivalent circuit of the junction transistor. All network components are expressed in terms of the physical parameters of the transistor. This network has been used to calculate Mason´s U-function, which in turn gives the highest frequency at which a transistor can give a power gain. From the derived formula, it is possible to see how the physical parameters interact to limit the frequency response. The design requirements for a given maximum frequency can be obtained from the formulas; a few examples are discussed. The accurate equivalent circuit will be helpful in designing transistors for more specialized applications.