- In bipolar junction transistor (BJT) configuration it requires two ports network namely input port and output port.
- The input port are require 2 input terminal and the output port require 2 output terminal therefore it requires 4 terminals due to it is called as 2-port, 4-terminal network.
- There is a common terminal for an input port and output port. Then there will be only 3 terminals instead of 4 terminals in this 2-port due to this is called a 2-port, 3 terminal network it shown above fig.
- The BJT has only three terminal namely an emitter, base and collector.
- When a transistor is to be connected in circuit like a 2-port, 4 terminals, it is not possible because it has only three terminals e.g. emitter, base and collector.
- This difficulty is overcome by treating one of the three terminals as a common terminal to input port and output port.
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